A door closer that integrally incorporates a door-opening-assistance device, and that therefore eliminates the need for unnecessary troublesome adjustment between parts, and whose number of parts is reduced, making said door closer compact. The door closer 1 includes a closer 1a that includes a pinion 5 that rotates in the forward and reverse directions when the door is opened or closed, respectively. A cylinder 9 is meshed with the pinion 5 and moves forward and backward. A closing spring 14 energizes the door in the closing direction via the cylinder 9and the pinion 5. A opening-assistance device 1b that includes an opening spring 22 that stores an opening force in the door-opening direction due to the movement of the cylinder 9 when the door is opened. Locking mechanisms 27, 28, and 29, that—when the door is opened—lock the opening spring 22 under an opening-force-storing condition. An unlocking mechanisms 23 and 24 that—when the door is closed—unlock the locking mechanisms. The closer 11a and the door-opening-assistance device 1b are inside the same case 6 and interlinked by the opening of the door.