Generalized pustular psoriasis is a distinct type of psoriasis characterized by recurrent febrile attacks with disseminated subcorneal pustules on generalized skin rashes. Recently, homozygous and compound heterozygous mutations of the IL36RN gene, which encodes the anti-inflammatory cytokine interleukin (IL)-36 receptor antagonist, were identified in familial and sporadic cases of various ethnicities with generalized pustular psoriasis. Here we report a 39-year-old Japanese male patient who had suffered from repeated attacks of generalized pustular psoriasis since infancy with intervals of several years. At presentation, erythematous lesions with a few pustules were found only on some parts of the body and controlled with topical corticosteroids. An analysis of the IL36RN gene revealed compound heterozygous mutations of c.28C>T and c.368C>T. While the former mutation causing the premature termination p.Arg10X is recurrent in Japanese cases, the latter missense mutation causing p.Thr123Met substitution is novel, but another mutation in the same position has been reported in one Japanese case. Our report further supports the presence of the Japanese-specific hot spots in the IL36RN gene, 28C and 368C, and suggests the functional significance of Thr123. This special type of generalized pustular psoriasis caused by IL36RN mutations has been designated as deficiency for IL-36 receptor antagonist, a new hereditary autoinflammatory disease, and its phenotypes have emerged to include other related pustular disorders, palmoplantar pustulosis, acrodermatitis continua of Hallopeau, and acute generalized exanthematous pustulosis. The genetic analysis of the cases with these diseases would be important for establishment and application of the specific treatments targeting the IL-36 signaling.