A fuel cap of the invention has a torque mechanism that transmits a rotational torque to a casing main body via engagement of a first torque arm of a torque plate with a handle engagement element, in response to rotation of a cover in a closing direction. When the rotational torque exceeds a predetermined level, the engagement is released to give a click. The first torque arm is constructed as a cantilever beam having a free end that is arranged to face an arm support member across a preset gap. Under application of pressure from the handle engagement element, the first torque arm is deformed in a direction perpendicular to a longitudinal axis of the first torque arm at a two-point support where the free end is in contact with the arm support member, and transmits a rotational torque in the closing direction to the casing main body. This arrangement of the invention assures setting of the rotational torque of the torque mechanism to the predetermined level to apply a sufficient sealing stress to the fuel cap.