Recent progress in application of magnetic regenerator material provides a potentially new technology for the cryogenic field. In the present review, the simple theoretical background of the application is given from the point of view of the magneto-caloric effect. The basic researches on physical properties, mechanical properties and fabrication methods regarding magnetic regenerator materials are introduced. This review describes the development of 4K Gifford-McMahon (GM) refrigerator and other small refrigerators using magnetic regenerator materials, and shows the activities on application of 4K-GM refrigerator to many cryogenic systems, such as superconducting magnet systems and superconducting device systems. Finally, this review points out the wide variety of possibile applications, and discusses some problems awaiting solution at next stage.