To improve the bearing performances such as a quietness, a fretting durability in the shock and the vairation in the transporting time and the operation time of the apparatus, and a sound durability, at a low cost.

While a track wheel is composed of a bearing steel, a Cr infiltration process is applied to a rolling element made of steel, and the Cr is dispersing infiltrated from the surface, so as to form a surface hardened layer including the Cr more than 30%, perferably more than 50%, to its surface, and the sound durability and the antifretting durability are improved extensively, while securing the quietness same as or more than the SUJ 2.