This study is an open-label, non-controlled study to evaluate the efficacy and safety of KHK4827 in subjects with pustular psoriasis (generalized) and psoriatic erythroderma. Pharmacokinetics of KHK4827 will also be assessed.

Inclusion Criteria:

• Subject has signed voluntarily the written informed consent form to participate in this study.
• Subject has been diagnosed as pustular psoriasis or psoriatic erythroderma.
• Subject has received at least one previous phototherapy or systemic psoriasis therapy or has been a candidate to receive phototherapy or systemic psoriasis therapy in the opinion of the investigator.

Exclusion Criteria:

• Subject with psoriatic erythroderma has involved Body surface area (BSA) of lesion < 80% at baseline.
• Subject diagnosed with guttate psoriasis, medication-induced or medication-exacerbated psoriasis.
• Evidence of skin conditions at the time of the screening visit (eg, eczema) that would interfere with evaluations of the effect of KHK4827 on psoriasis.
• Subject has any active Common Terminology Criteria for Adverse Events (CTCAE) grade 2 or higher infection
• Subject has a significant concurrent medical condition or laboratory abnormalities, as defined in the study protocol.
• Subject has used Ultra Violet B (UVB) therapy within 14 days of the first dose or Ultra Violet A (UVA) (with or without psoralen) within 28 days of the first dose.
• Subject has used etanercept, adalimumab, infliximab or ustekinumab within 1 week, 2 weeks, 8 weeks or 12 weeks of the first dose, respectively.
• Subject has stopped ustekinumab or other anti-Interleukin (IL)-23 biologics therapy due to lack of efficacy
• Subject has used live vaccine within 3 months of the first dose
• Subject has previously used an anti-IL-17 biologic therapy