[en] A number of formulations have been proposed for inelastic analysis, particularly for the thermal elastic-plastic creep analysis of nuclear reactor components. In the elastic-plastic regime, which principally concerns with the time independent behavior, the numerical techniques based on the finite element method have been well exploited and computations have become a routine work. However, the establishment of the constitutive relations is still an important task. Therefore, a computer program should be designed and developed with sufficient generality so that it allows for the novel constitutive equations which may be proposed from the side of material scientists interested in the micro-mechanisms of plastic deformation. With respect to the problems in which the time dependent behavior is significant, it is desirable to incorporate a procedure which is workable on the mechanical model formulation as well as the method of equation of state proposed so far. A computer program should also take into account the strain-dependent and/or time-dependent micro-structural changes which often occur during the operation of structural components at the increasingly high temperature for a long period of time. The present paper introduces a rational updated formulation and a computer program under development by taking account of the various requisites stated above. Numerical examples include 1) thermal elastic-plastic creep deformation of a thick walled cylinder, 2) numerical experiments on the tensile instability of uniaxial test specimens and 3) typical examples from the activities of JSME (Japan Society of Mechanical Engineering) Committee on Research and Development of Inelastic Analysis Programs