A cap for bearing device is attached to one end portion of an outer race member in a bearing device to block an opening portion, and includes: a cylindrical part that is fitted to the outer race member; a lid part configured to block an end portion of the cylindrical part; an annular seal part configured to, when being fitted to the outer race member, be compressed between the cap for the bearing device and the outer race member; and a ventilation part, which, in the course of fitting the cylindrical part to the outer race member, allows air to pass between inside and outside of a bearing space, and in the state where the cylindrical part is fitted to the outer race member, the ventilation is shut down.