A Phase 2 Clinical Study to Explore the Optimal Dosage/Administration of PM012 Tablet in Alzheimer's Disease

Inclusion Criteria: * 1\) Male and female patients aged ≥ 50 and ≤ 85 years. * 2\) Patients clinically diagnosed as probable Alzheimer's disease based on DSM-IV and NINCDS-ADRDA criteria. * 3\) Patients between MMSE score of 20\~26 at screening visit. * 4\) Patients with Global CDR score of 0.5 or 1 at the screening visit. * 5\) Patients administered with donepezil 5㎎ stably for over 3 months or who have never been administered donepezil. * 6\) Patients who can perform cognitive or other necessary tests. * 7\) Patients who have a caretaker who can accompany the patient for all clinical visits and for the primary efficacy evaluation (a caretaker is a family member or someone trustworthy who provides care for daily activities, spending more than 8 hours per week with patients). * 8\) Patients who have consented to participate in medically acceptable contraception\* \* Effective contraception methods: Infertility surgery of the patient or his/her spouse (vasectomy, tubal ligation), placement of an intrauterine contraceptive device, double barrier method (concomitant use of spermicides and condoms, and contraceptive diaphragms, vaginal sponges, or cervical caps). Oral contraceptives and intermittent celibacy (absolute celibacy is allowed) are not acknowledged as effective contraceptive methods. * 9\) Patients who have signed the informed consent on his/her own will Exclusion Criteria: * 1\) Patients with hypersensitivity to the investigational product or components contained in the investigational product. * 2\) Patients with hypersensitivity to piperidine derivatives. * 3\) Patients with possible, probable or definite vascular dementia according to the NINDS-AIREN criteria. * 4\) History (cerebrovascular disease, structural or developmental malformations, epilepsy, contagious, degenerative, or infectious/demyelinating CNS status) and/or evidence (CT or MRI results performed at screening or within 12 months) of other CNS diseases as the major cause of dementia. * 5\) Patients who are illiterate. * 6\) Patients with severe hearing or visual disabilities so that efficacy assessment is impossible. * 7\) Abnormal test results for vitamin B12, serologic testing for syphilis, or thyroid stimulating hormone (TSH) that may have contributed to or may be the cause of patient's dementia. * 8\) Patients with a history of significant psychiatric disease such as schizophrenia or bipolar disorder that may interfere with participation in the trial as viewed by the investigator, or patients with current major depression disorder (Short Form GDS ≥ 7) (However, patients who depressed due to Alzheimer's disease can participate in this trial by the investigator). * 9\) Patients with genetic disorders such as galactose intolerance, Lapp lactase deficiency, or glucose-galactose malabsorption. * 10\) Patients with a history of known or suspected seizure including febrile seizure, or recent history of loss of consciousness or a history of significant head trauma with loss of consciousness. * 11\) Patients with gastrointestinal, endocrinological, or cardiovascular disorders that is not controlled by diet or drugs. * 12\) Patients with cardiac diseases such as myocardial infarction, valvular heart disease, or arrhythmia within 3 months prior to screening. * 13\) Patients with asthma or obstructive pulmonary diseases that is not controlled by drugs. * 14\) Patients with extrapyramidal disorders (Parkinson's disease, Parkinsonism, etc). * 15\) Patients with dementia due to Creutzfeldt-Jakob disease, Pick's disease, or Huntington's disease. * 16\) Patients with uncontrolled diabetes (HbA1c \> 8.0%) or insulin dependent diabetes. * 17\) Patients with a history of alcohol or other substance abuse. * 18\) Patients with hypertension with systolic pressure over 165mmHg or diastolic pressure over 96mmHg. * 19\) Patients with severe renal dysfunction (Serum creatinine over 2.0㎎/dl). * 20\) Patients with severe liver dysfunction (ALT, AST, total bilirubin more than 2.5-fold the upper normal limit). * 21\) Patient who has been administered drugs that Dementia drugs(Donepezil, Galantamine, Memantine, Rivastigmine tartrate) within 3 months prior to screening (However, patients who have been administered donepezil 5mg stably for over 3 months are excluded). * 22\) Patient who has required to take restricted drugs other than investigational products during the clinical trial period. * 23\) patient who has unabled to take concomitant drugs during the clinical trial period under the following conditions : It was taken without dose change 2 months before randomization, and was taken without dose change during the clinical trial period (except for drugs allowed to be taken as needed). * 24\) Patients with a history of clinically significant drug hypersensitivity reaction. * 25\) Patients who have been administered investigational products from another clinical trial within 3 months prior to participation in this trial. * 26\) Patients who are deemed unfit to participate in this trial by the investigator.