It is thought that the temperature range for operation of high-temperature superconducting (HTS) magnets is 20 to 50 K if the HTS magnets are made from rare-earth materials. An HTS wire made from rare-earth materials has several advantages in the high-temperature region close to 50 K. In this temperature region, single-stage cryocoolers are available. Therefore, we examined via tests the practicability of applying a pulse-tube cryocooler, which has advantages of simple structure, high reliability and simple maintenance, as cooling systems of on-board HTS magnets for the magnetic levitation train (Maglev). We have developed a high-efficiency cooling system that consists of multiple pulse-tubes and one compressor. When the two pulsetubes are operated in “reverse phase mode,” the cooling system has a large COP value. In this paper, we improved the performance of the multiple pulse-tubes system, and obtained a cooling capacity of 170 W at a temperature of 50 K, and a COP of 0.023.