Cryocooler

A cryocooler comprising:

• a compressor;
• an expander;
• a gas line that allows a working gas to be circulated between the compressor and the expander and includes a high pressure line through which the working gas is supplied from the compressor to the expander, and a low pressure line through which the working gas is collected from the expander to the compressor;
• a bypass line that connects the high pressure line to the low pressure line such that the working gas bypasses the expander and returns from the high pressure line to the low pressure line;
• and
• a bypass flow rate control unit that controls a flow rate of the working gas flowing in the bypass line to provide pressure control of the gas line,
• wherein the bypass line includes
• a variable flow rate bypass that includes a flow rate control valve and connects the high pressure line to the low pressure line, and
• a fixed flow rate bypass that includes an on/off valve and connects the high pressure line to the low pressure line in parallel with the variable flow rate bypass, and
• the bypass flow rate control unit controls the flow rate of the working gas flowing in the bypass line through a combination of opening degree adjustment of the flow rate control valve and switching of the on/off valve.