To provide a bolt head part capable of preventing the other object in contact with it from being damaged and realizing theft prevention.

This bolt head part is constituted by connecting a head part and a screw part mutually and is provided with a plurality of semi-spherical recessed parts in the head part. The head part itself provided with the plurality of semi-spherical recessed parts is semi-spherical. The head part is composed of a semi-spherical part and is provided with the plurality of semi-spherical recessed parts being smaller than the head part. The maximum circumferential part of the semi-spherical head part has a gentle curved face, and the plurality of semi-spherical recessed parts are provided on the semi-spherical head part. Two to six semi-spherical recessed parts are provided in the head part, and dimension of the plurality of semi-spherical recessed parts in the head part is arbitrarily changed.