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 1st regenerator in the first cylinder and accommodating heat regenerating material (HRM) 1; and a second regenerator in the 2nd cylinder accommodating HRM 2, HRM 2 including HRM particles, each HRM particle including a metal element and a heat regenerating substance including an oxide or oxysulfide and having a maximum specific heat at ≤20 K of ≥0.3 J/cm3·K; each HRM particle including a 1st and 2nd region, the 2nd region being closer to each HRM particle's outer edge than the 1st, and the 2nd region having a higher metal element concentration than the 1st, the 1st and 2nd region containing the heat regenerating substance.