A wave-gear-type linear-actuation mechanism comprises a flat-type wave gear; a lead screw that is a structural component of the wave gear and is formed on an outer peripheral surface of a first circular spline; and a linear-actuation cylinder threaded onto the lead screw, a linear-actuation cylinder 4 having a screw groove that is formed in an inner peripheral surface thereof. It is possible to obtain a linear-actuation mechanism whose holding force during reverse input mode (speed increasing mode) is higher than cases where a cup-type flexible screw is used.