Positive clutch

An object of the invention is to provide a positive clutch that has a high rigidity and simple structure, and offers potential to allow easy adjustment of torque limit load, suppress friction loss and noise generation, realize a size reduction, and extend the service life. This positive clutch is configured to prohibit relative rotation of an outer and inner races by circumferentially holding each of a plurality of rollers between an outer race slope portion and an inner race slope portion. The clutch includes a torque limiter mechanism, which includes a piston member having a flat portion that forms the outer or inner race slope portion, and a resilient member that applies a constant load on the piston member. The piston member is slidably accommodated in a piston member accommodating hole formed in the outer race or the inner race.