PURPOSE: To improve starting performance by providing a displacer rod in the displacer piston of a free type stirling engine while it can move reciprocally whereby effecting a reciprocal movement at the time of engine start by means of a linear motor contained in the displacer.

CONSTITUTION: A cylinder 3 is provided in the displacer 1 of a free piston type stirling engine, and a piston 5 attached to the end of a displacer rod 2 is secured in the cylinder while it can move reciprocally. Coils 9, to which electric current is sent from the outside, are provided in the grooves of the piston 5, and a magnet 11 is provided to the cylinder 3. When electric current is applied to the coil 9 at the time of engine start, as both of the coil 9 and the magnet 11 comprises a linear motor 12, vibration is produced. And this vibration causes working gas in the upper and lower sections of the displacer 1 to start actions of heating, reconditioning, and cooling within a gas passageway for having the stirling engine started easily.