To provide a Stirling engine to cause no collision between a piston and a displacer even when the engine is operated on a high input condition right after a start of operation and to provide its operation method.

The Stirling engine comprises: a piston 3 fitted in a cylinder 1 filled with working gas and driven by a drive means 7 for reciprocation; a displacer 2 fitted in the cylinder 1 and reciprocated with a phase difference with that of the piston 3; a compression chamber 4 partitioned between the piston 3 and the displacer 2; an expansion chamber 5 positioned on the opposite side to the compression chamber 4 with the displacer 2 nipped therebetween; and a heater 17 to promote a temperature difference between a working gas temperature in the compression chamber 4 and working gas temperature in the expansion chamber 5 during non-steady operation motion right after starting of operation.