To provide a press-fit auxiliary tool of a push nut capable of extremely easily and favourably carrying out press-fitting operation of the push nut and precisely carrying out the press-fit operation in pushing depth by matching a mounting hole and a shaft center with each other.

This press-fit auxiliary tool is fundamentally constituted of a spiral part 1 for drawing free to be properly screwed in a female screw part 11 of a push nut 10 and an auxiliary tool main body 2 projectively provided on its head end part. The auxiliary tool main body 2 is constituted of a small diametrical part 2a on the side of the spiral part 1 for drawing and a large diametrical part 2b outside of it, and a hexagonal hole 3 is formed on an outer and surface of the large diametrical part.