The pulse tube refrigerator, which has made great progress in the past couple of years, is a typical thermoacoustic device and has attracted attention because it may be replacing conventional cryocoolers, such as Stirling and Gifford--McMahon refrigerators. The pulse tube refrigerator is a very interesting system from the viewpoint of thermoacoustics because it consists of a regenerator where entropy is pumped with a reversible process by the progressive wave component of the oscillation, and a pulse tube where work flows adiabatically. A four-valve-type single-stage pulse tube refrigerator was constructed, which has a pressure switching valve system at the hot end of the pulse tube with a conventional GM compressor unit. The four-valve type is an active and easy way to evaluate the boundary condition of phase and displacement quantitatively. By the optimization of the phase shifting, driving conditions, and the shapes, the lowest temperature of 30 K and cooling power of 10 W (at 80 K) for 700 W of power consumption are obtained, at present. The key point of achieving higher performance is how to reduce the work dissipation in the regenerator and the heat transfer losses via the pulse tube. In this session, an actual approach to this viewpoint will be discussed.