To constitute a hydraulic pressure cylinder block piston by two differential materials.

This hydraulic pressure cylinder block piston is a piston for using in a cylinder block of a hydraulic pressure power unit, and is has an elongated cylindrical main body and one end part as a spherical surface. The piston comprises a main body and an insert, and the main body and the insert are manufactured by differential materials, preferably, metallic materials, and are joined integratedly with each other. The piston main body is formed in a shape of a solid cylindrical body or a hollow cylindrical tube. Furthermore, the spherical surface is formed in a shape of an inside spherical socket or an outside spherical ball. In the insert, a piston of an opening cavity is formed in an elongated shape, and a piston structure of a closed cavity is formed in a short shape. The piston crosses the main body and the insert, and is provided with a guide passage as a passage for a pressurizing fluid.