To provide a highly reliable regenerator for a Stirling engine capable of preventing a performance from lowering even under hot environment.

This regenerator 1 is disposed between a compression space 14 and an expansion space 15 in the Stirling engine, becomes a flow passage for working gas reciprocating between both spaces 14 and 15, and collects or discharges heat quantity from the working gas. The regenerator 1 not causing thermal contraction under hot environment can be formed by applying a heat treatment to a resin film 2 as the material of the regenerator 1 beforehand. The lowering of the performance of the Stirling engine having the generator 1 does not occur even if positioned and operated in the hot environment for a long time, the performance generally equal to that at the beginning can be maintained, and thus the highly reliable Stirling engine can be provided.