A door opener includes a main bracket, a locking element, a compression spring, a rotation plate, and a torsion spring. The main bracket includes a lower plate and a first sidewall and a second sidewall oppositely positioned at edges of the lower plate. A guide rail and a resisting portion extend from the first sidewall opposite to the second sidewall. The first sidewall defines a through hole thereon. The locking element includes a sliding bar and a spacing block extending from a side of the sliding bar, the sliding bar supported on the guide rail, and the spacing block passing through the through hole. The compression spring is sleeved on the guide pole. The rotation plate is rotatably received in the main bracket, and a fixing block for latching with the spacing block extends from the rotation plate. The torsion spring resists the rotation plate and the lower plate.