A steel retainer (3), which retains needle rollers (2), is formed from a steel plate containing 0.15 to 1.10% by mass of carbon. After being formed, the steel plate is subjected to induction heat treatment which includes induction hardening and induction tempering. Such heat treatment can be carried out efficiently in a short period of time, using compact treatment facilities, even in small-lot production. The retainer (3) thus formed is sufficiently resistant to wear and surface damage, and is high in fatigue strength and fracture strength as a whole.