Steady thermal stress analysis without heat generation can easily be solved by the boundary element method. However, for the case with heat generation, the domain integral is necessary. This paper shows that the problem of steady thermal stress with heat generation can be solved approximately without the domain integral using an improved multiple-reciprocity boundary element method. In this method, the domain integral in each step is divided into point, line, and area integrals in the case of a two-dimensional problem. In order to solve the problem, the contour lines of heat generation, which approximate the actual heat generation, are used.