Disclosed is a clearance control swash plate device for a transmission or reducer and a single-shaft two-speed drive system, including the clearance control swash plate device, with a friction clutch. The clearance control swash plate device includes: an action plate mounted on a power transfer shaft; a first thrust bearing disposed on the action plate, and configured to prevent rotation force, received from the action plate, from being transferred; a first clearance swash plate disposed on the first thrust bearing; a second clearance swash plate disposed on the first clearance swash plate; a worm engaged with a worm gear formed on the outer circumference of the second clearance swash plate; a second thrust bearing disposed on the second clearance swash plate, and configured to prevent rotation force, received from the second clearance swash plate, from being transferred; and a thrust washer disposed on the second thrust bearing.