An auxiliary machine-driving device for a vehicle, comprising: an engine that generates a drive torque; a first auxiliary machine that is driven by the engine; a motor/generator that is driven by the engine; an engine roller that integrally rotates with a crankshaft of the engine; a first rotating roller that integrally rotates with a rotary shaft of the first auxiliary machine; a second rotating roller that integrally rotates with a rotary shaft of the motor/generator; a first idler roller that is disposed between the engine roller and the first rotating roller; a second idler roller that always makes contact with the outer peripheral surfaces of the first rotating roller and the second rotating roller; a third idler roller that is disposed between the second rotating roller and the engine roller; and a linking mechanism that is driven by one actuator and that simultaneously changes the positions of the first idler roller and the third idler roller so as to switch between a state in which the first idler roller makes contact with outer peripheral surfaces of the engine roller and the first rotating roller, and the third idler roller makes contact with the engine roller and the second rotating roller at the outer peripheral surfaces, and a state in which the first idler roller is separated from the engine roller and the first rotating roller, and the third idler roller is separated from the engine roller and the second rotating roller, wherein the direction of rotation of the second rotating roller is the direction of rotation in which a wedging effect acts on the third idler roller when starting the engine with a drive torque of the motor/generator; and the engine roller rotates in a direction of rotation that is a direction of rotation in which a wedging effect acts on the first idler roller when driving the first auxiliary machine with the drive torque of the engine. an engine that generates a drive torque; a first auxiliary machine that is driven by the engine; a motor/generator that is driven by the engine; an engine roller that integrally rotates with a crankshaft of the engine; a first rotating roller that integrally rotates with a rotary shaft of the first auxiliary machine; a second rotating roller that integrally rotates with a rotary shaft of the motor/generator; a first idler roller that is disposed between the engine roller and the first rotating roller; a second idler roller that always makes contact with the outer peripheral surfaces of the first rotating roller and the second rotating roller; a third idler roller that is disposed between the second rotating roller and the engine roller; and a linking mechanism that is driven by one actuator and that simultaneously changes the positions of the first idler roller and the third idler roller so as to switch between a state in which the first idler roller makes contact with outer peripheral surfaces of the engine roller and the first rotating roller, and the third idler roller makes contact with the engine roller and the second rotating roller at the outer peripheral surfaces, and a state in which the first idler roller is separated from the engine roller and the first rotating roller, and the third idler roller is separated from the engine roller and the second rotating roller, wherein the direction of rotation of the second rotating roller is the direction of rotation in which a wedging effect acts on the third idler roller when starting the engine with a drive torque of the motor/generator; and the engine roller rotates in a direction of rotation that is a direction of rotation in which a wedging effect acts on the first idler roller when driving the first auxiliary machine with the drive torque of the engine.