Phase 2 Study of KHK4577

Inclusion Criteria: * Subject has signed voluntarily the written informed consent form to participate in this study. * Subject has been diagnosed as atopic dermatitis according to Guidelines for Management of Atopic Dermatitis (2009). * Rajka \& Langeland criteria of \>/= 4.5 at screening visit * Investigator's Global Assessment (IGA) score of \>/= 3 at screening visit Exclusion Criteria: * Evidence of skin disorders/conditions that would interfere with the assessment of the effect of the study drug. * Subject received photochemotherapy or systemic immunosuppressants within 2 weeks prior to informed consent. * Subject has any active infectious disease(except localized infection) which needs to treat with systemic antibiotics(eg. antibacterial, antifungal or antiviral drugs) within 4 weeks prior to informed consent. * Subject has complications / history of drug abuse or alcoholism. * Subject has drug allergy or history of allergic reaction to a drug medicine. * Subject has a significant concurrent medical conditions as defined in the study protocol. * Subject is breast-feeding, pregnant or planning to become pregnant in this study period.