To provide a brake mechanism capable of obtaining stable braking torque and releasing a brake by a simple mechanism.

A tapered roller 2 held by a retainer 3 is moved from a radial axis 6 and pressed against faces having tapered faces of a rotor 12 and a rotor 13 relatively rotating around an axis 7 and a stopper 4 is inserted on the axis 7 of a rotational center so as to prevent a roller shaft 2a from radially returning. In between the tapered faces and the roller, slipping occurs and a frictional force is generated by a difference in peripheral velocities of inner and outer diameter parts, and this acts as a brake. By removing the stopper 4, the tapered roller 2 radially moves, an axial distance between the two relatively rotating faces 5 becomes small, a bearing mechanism by a ball 1 actuates, and the braking force is released.