To provide a door opening/closing device which structurally enables a door body to have a sufficient bearing capacity against a heavy load, even if the heavy load is imposed on the door body in the opening/closing of the door body or horizontal adjustment.

When an adjusting bolt 11 is made to advance/recede in a proper direction in the movement of the door body 4 by the horizontal adjustment of the door body 4 with respect to a fixing member 2, a mounting plate 10 is moved in the direction of an arrow, shown in Fig., along with the advance/receding of the adjusting bolt 11 by making a position of a connection member 13 serve as a supporting point. In this movement, the sufficient bearing capacity can be held because the following load is borne by the connection member 13 though the mounting plate 10 is subjected to the load from the mounting plate 5. Additionally, the sufficient bearing capacity can be held, because the heavy load, which is applied to the door body 4 in the opening/closing of the door body 4 after adjustment, can be borne by the connection member 13, though the heavy load is transmitted to the mounting plate 10 via the mounting plate 5 and the mounting plate 10 is subjected to the load in the direction of the arrow.