To provide a guide structure of a child seat attaching part to be inserted/attached to a seat without forming a notch and to be attached without deteriorating the outer appearance when a child seat is not attached to the seat.

The guide structure of the child seat attaching part 5 can guide a lock member 6 mounted on the rear part of the child seat to the child seat attaching part 5 mounted on the seat 1. A guide member 11 has an upper cover 14 and a lower cover 15. The guide member 11 can be inserted/attached to the child seat attaching part 5 with the upper cover 14 and the lower cover 15 closed, and by opening the upper cover 14 and the lower cover 15 while the guide member is inserted/attached to the child seat attaching part 5, the lock member 6 mounted on the rear part of the child seat can be guided.