A cryocooler, includes a cylinder filled with gas. A piston rectilinearly reciprocates inside of the cylinder and compresses or expands the gas. A connecting rod has a first side coupled to the piston and moves with the piston, and a second side having a first thread along an outer circumference thereof. A linear motor rectilinearly reciprocates a motor shaft toward the connecting rod in accordance with a control signal. A sleeve has two open sides, so that an end portion of the motor shaft can be supported by and inserted in one open side, and the second side of the connecting rod can be inserted in the other open side, and an inner circumference of the sleeve is formed with a second thread that engages with the first thread of the connecting rod and rotates to adjust a distance between the motor shaft and the connecting rod.