To provide an outdoor unit for an air conditioner improving maintainability while minimizing the generation of vibration and noise by reinforcing posts for connecting a top plate to a bottom plate without using another member.

The bottom plate 1 and the top plate 7 are connected by a first post 14, a second post 15, a third post 17 and a fourth post 16. The second post 15 located near an electric equipment box 13 is moved backward from a body corner and installed while the edge of the bottom plate 1 is provided with a reinforcing piece 1b cut and raised in a substantially triangular shape, and the reinforcing piece 1b is screwed to the front face side of the second post 15. Consequently, even if the second post 15 is moved backward and installed, vibration and noise generation to an outdoor unit can be minimized to perform silent operation without causing the insufficiency of support strength. Further, the maintenance and inspection work of the outdoor unit can be easily performed.