To provide a jig for mounting auxiliary machines and an auxiliary machine mounting method using the jig capable of mounting auxiliary machines to an engine while easily securing pulley alignment accuracy of the auxiliary machines.

Pulleys 113, 123, 133 of auxiliary machines 111, 121, 131 are fixed to pulley engagement parts 31, 41, 51 for auxiliary machines of a jig 1 for mounting auxiliary machines in advance, and a crank pulley engagement part 20 is engaged with a crank pulley 103 of an engine 101. Accordingly, the pulley 113, 123, 133 of each auxiliary machine 111, 121, 131 is aligned relative to the crank pulley 103, and the auxiliary machines 111, 121, 131 can be mounted to the engine 101 while the alignment accuracy of the pulleys 113, 123, 133 is secured. Thus, an auxiliary machine mounting operation is simplified and its efficiency is increased, resulting in the elimination of the need for the troublesome alignment adjustment of the pulleys 113, 123, 133 of the auxiliary machines 111, 121, 131, and the burden on a worker is reduced.