To provide a door closer that prevents hydraulic oil from leaking out and enables smooth opening operation of a door.

A door closer 1 has a housing 3 comprising a sealed space 3a filled with hydraulic oil and an oil passage hole 7, and the sealed space 3a has a reciprocatably disposed piston 4 as energized by one end of a coil spring 5, a rack and pinion mechanism 9 disposed outside the piston 4, and a rotation shaft 12 coupled to the rack and pinion mechanism 9. In the sealed space 3a, an expansion absorption member 13 is disposed as incapable of contacting with the oil passage hole 7. The expansion absorption member 13 regulates the position of another end 5b of the coil spring 5 when the door closer is assembled.