To provide a valve driving device that reduces noise generated by a timing chain and a sprocket in an engine having a plurality of cylinder heads.

A valve driving device for driving valves provided for each of a plurality of cylinder heads 2 and 3 in an engine 1 includes: first cam sprockets 21 and 31 that are mounted to cam shafts provided for a first cylinder head; second cam sprockets 41 and 51 that are mounted to cam shafts provided for a second cylinder head; crank sprockets 11 and 12 that are fixed to a crank shaft; and a first chain 80 and a second chain 100 that transmit driving force to each of the first cam sprockets and the second cam sprockets from the crank sprockets or an idler sprocket 72 linking with the crank sprockets. The number of teeth of the first cam sprockets is different from the number of teeth of the second cam sprockets.