To provide an engine accessory driving device that changes a rotation speed of an engine accessory according to an engine load state.

The engine accessory driving device includes: a low-speed ratio transmission mechanism 3 for receiving the rotation of an engine 2 at a low speed ratio; a high-speed ratio transmission mechanism 4 for receiving the rotation of the engine 2 at a high speed ratio; and a switching mechanism 6 that connects, in a low-load operation of the engine 2, the engine accessory 5 to the low-speed ratio transmission mechanism 3, and connects, in a high-load operation of the engine 2, the engine accessory to the high-speed ratio transmission mechanism 4.