A free piston Stirling refrigerator of the present invention has a cylinder provided inside a casing; a piston and a displacer that are provided in a way such that they are capable of reciprocating inside the cylinder; a linear motor for reciprocating the piston; and a control unit for controlling the operation of the linear motor. Particularly, the control unit has an inverter circuit for generating an alternating current with a given frequency and then supplying the alternating current to the linear motor; a current detection circuit for detecting the current outputted from the inverter circuit; and a control circuit for controlling the output from the inverter circuit based on a turbulence in the current detected by the current detection circuit. Thus, collisions between the piston and the displacer (i.e. hitting) can be restricted through an inexpensive configuration and a simple control.