A rotary valve mechanism of a cryocooler includes a valve rotor and a valve stator. A rotor recessed portion is formed such that the rotor recessed portion fluidally communicates with a stator recessed portion at a first opening degree at a second phase of a valve rotation. The valve rotor includes a first rotor communication groove and/or a second rotor communication groove formed in the valve rotor such that the rotor recessed portion fluidally communicates with the stator recessed portion at an opening degree which is smaller than the first opening degree at a first phase preceding the second phase, and/or the valve stator includes a stator communication path formed in the valve stator such that the rotor recessed portion fluidally communicates with the stator recessed portion at an opening degree which is smaller than the first opening degree at the first phase preceding the second phase.