A sealing structure seals a clearance between a housing and a brake rotor. The housing defines a fluid chamber for sealing a magnetic viscous fluid inside. The brake rotor penetrates through the housing and generates brake torque by contacting the magnetic viscous fluid. The housing has a magnetic sleeve section and a magnetic screw section provided to the brake rotor. The magnetic sleeve section is continuous in a rotational direction of the brake rotor and generates a magnetic flux. The magnetic screw section is an external screw having a screw thread, which extends away from a fluid chamber side toward a phase adjusting mechanism side when traced in a rotational direction of the brake rotor. The magnetic flux is guided to the magnetic screw section through a sealing gap between the magnetic screw section and an inner peripheral section of the magnetic sleeve section.