A pulse tube cryocooler is furnished with a second-stage cooling stage and an insert. The second-stage cooling stage has a lateral-surface opening, and a first heat-exchange surface extending in a sideways direction from the lateral-surface opening into the second-stage cooling stage. The insert includes a base-end portion fixedly fitted into the second-stage cooling stage to plug the lateral-surface opening, and a second heat-exchange surface that extends in the sideways direction from the base-end portion and is disposed inside the second-stage cooling stage, opposing the first heat-exchange surface. Between the first heat-exchange surface and the second heat-exchange surface the insert forms a clearance that flows a working gas, bringing both the first heat-exchange surface and the second heat-exchange surface into contact with the working gas.