A first fixing portion of a generally L-shape is provided in one side of a box and a first attachment portion is provided in a first fixing member to which the box is attached corresponding to the first fixing portion. The first fixing portion of the box is engaged with the first attachment portion of the fixing member. The first fixing portion is provided in the one side of the box and a second fixing portion equipped with a flexible arm is provided in other side of the box. A second attachment portion is provided in the fixing member corresponding to the second fixing portion and the second fixing portion of the box is engaged with the second attachment portion of the fixing member, and where the flexible arm formed outward the box is bent. A moving regulating portion to regulate the moving for transverse and longitudinal directions for the second attachment portion is provided in the second fixing portion. Thus, a fixing structure of a box is provided which is easily attached to an opponent fixing member and is easily detached from it.