To provide an outdoor unit installing apparatus for an air conditioner capable of easily fixing an outdoor unit in which a supply grill is mounted on a front surface from an installing window.

An engaging hole 4e corresponding to a locking piece 3a of the outdoor unit 3 is provided at a side face of a coupling fixture 4b. Meanwhile, the piece 3a made of a steel sheet welded to right and left sides of the bottom of the outdoor unit 3 and projected in a front surface direction of the outdoor unit 3 is provided. The outdoor unit 3 is pressed from the window 1 toward the fixture 4b, the piece 3a is inserted into the hole 4e of the fixture 4b, and the forward side of the outdoor unit 3 is coupled. A fixed piece 3c welded to right and left bottoms of the outdoor unit 3 and projected rearward is provided on the back surface of the outdoor unit 3. After an insertion hole 3d provided near the center of the piece 3c and insertion holes 4d provided at the bottoms of the right and left fixtures 4c are matched, clamping bolt 6 is inserted into the two holes, and a nut 7 and the bolt 6 are engaged to clamp the back surface side of the outdoor unit 3.