To provide a door mounting structure for easily and accurately mounting a door on the opening end of a storage box without a gap in its pivoting part for preventing dust or the like from coming in and for stopping the door at a desired degree of opening.

In structuring this door mounting structure, the plate base part 1a of a bearing member 1 which is as long as the opening width of a storage box A is fixed at the lower face of a top panel at the opening end of the box A, the round rod-shaped hinge shaft 2a of a shaft member 2 is freely turnably fitted in the bearing hole 1c of the bearing whose cross section is C-shaped in the total length at the front end lower face of the base part 1a and the upper end of a door body 3 is joined at the lower end of a frieze board piece 2b protrusively and downwardly provided over the total length of the shaft 2a. The door body 3 is opened and closed without a gap in the pivoting part by the hole 1c and the shaft 2a. Moreover, the door body is closed at a desired degree of opening by the friction between the hole 1c and the shaft 2a.