Abstract The Japanese Prototype Fast Breeder Reactor Monju is now at a stage of submitting applications to the government for getting Construction Permission. Detailed structural design of components is now in progress. As well understood, a number of components of Monju have to be subjected to elevated temperature design. For this need, Power Reactor and Nuclear Fuel Development Corp. has developed “Elevated Temperature Structural Design Guide for Class 1 Components of Prototype Fast Breeder Reactor” (ETSDG). It is now incorporated into “Construction Code for Prototype Breeder Reactor”. The basic concept of ETSDG is originated from ASME Boiler and Pressure Vessel Code Section III, Case Interpretation N-47, ETSDG prepares some extended simplified inelastic analysis methods in addition to the basic concept of N-47. This extension is necessary to make easy the complicated inelastic analyses. The simplified methods have been developed through many case studies with detailed inelastic analyses, elastic analyses and experimental verifications.