To surely prevent toner from being leaked out from the toner storing space of a developing unit with inexpensive structure.

A bearing 49 press-fit in an fitting hole 48 formed on a case wall 11a surrounding the toner storing space 16 is equipped with a bearing main body 50, an elastic member 51, and a bearing seal 52. The dimension (a) of the outside diameter of the member 51 is larger than the dimension (b) of the inside diameter of the hole 48 and is enough to press-fit the bearing 49 in the hole 48, so that the outer peripheral surface of the member 51 is brought into contact with the inner peripheral surface of the hole 48 when the bearing 49 is press-fit in the hole 48. The dimension (c) of the inside diameter of the hole part 54 of the seal 52 is smaller than the dimension (d) of the outside diameter of a rotary shaft 19a and is enough to insert the shaft 19a through the bearing 49, so that the outer peripheral surface of the shaft 19a is brought into contact with the inner peripheral surface of the hole part 54 when the shaft 19a is inserted through the bearing 49. Thus, the toner is surely prevented from being leaked out from the space 16 with inexpensive structure.