To provide a temporary fixing mechanism capable of temporarily fixing a bolt without requiring a special member.

A shaft 2 is formed at the head part 1 of the bolt B, and a male screw part 4 is formed on the shaft 2. A non-screw part 3 is formed on the shaft starting at the head part 1 to the start point 4a of the male screw part 4, a through hole 6 for passing the shaft 2 of the bolt B therethrough is formed in a plate member 5 to be temporarily fixed, and a female screw part 7 maintaining such a dimensional relation that is threaded with the male screw part 4 is formed on the inner periphery of the through hole 6. The non-screw part 3 is so formed that its outer diameter R1 is smaller than the inner diameter R2 of the female screw part 4, and the axial length L1 of the non-screw part 3 is formed longer than the axial length L2 of the through hole 6 so that the male screw part 4 is passed through the female screw part 7 and the non-screw part 3 is positioned in the female screw part 7 while the male screw part 4 is threaded with the female screw part 7.