To provide an accessory mounting structure for an internal combustion engine, capable of driving an accessory 30 without being influenced by the condition of operating the internal combustion engine 2 while maintaining the total length and width of an engine unit 4.

The accessory mounting structure for the internal combustion engine comprises the internal combustion engine 2 having a crank shaft 9, a transmission device 3 connected to a first side face 13 of the internal combustion engine 2, and a first accessory 20 and the second accessory 30 provided in a space between the first side face 13 and a side face 16 of the transmission device 3. The first accessory 20 which can generate power has a first power transmitting means 40 for transmitting power between the first accessory 20 and the second accessory 30, and a second power transmitting means 50 for transmitting the power of the crank shaft 9 to the first power transmitting means 40 and either the first accessory 20 or the second accessory 30. The second power transmitting means 50 has a power cutoff mechanism 60 for cutting off the transmission of the power.