A two-stage heat regenerating cryogenic refrigerator may include: a vacuum vessel; a first and second cylinder in the vessel; the second cylinder coaxially connected to the first cylinder; a first regenerator in the first cylinder, the first regenerator accommodating heat regenerating material (HRM) 1; and a second regenerator in the second cylinder accommodating HRM 2, HRM 2 including plural HRM particles, each HRM particle including a heat regenerating substance having a maximum value of specific heat at a temperature of 20 K or less of 0.3 J/cm3·K or more and a metal element; each HRM particle including a first and second region, the second region being closer to each HRM particle's outer edge than the first, and the second region having a metal element higher concentration than the first, the first and second region containing the heat regenerating substance, and the heat regenerating substance contains an oxide or oxysulfide component.