To provide a door closer for opening a door by light force, reducing door closing force without delaying when a person opens the door.

This door closer has a door closing force generating means, a door closing force adjusting means for increasing and decreasing the door closing force, a detecting means for detecting an opening-closing state of the door and an increasing-decreasing state of the door closing force, and a control means for forming a control signal for operating the door closing force adjusting means, that is, the control means for generating a signal for reducing the door closing force when closing the door by generating a signal for increasing the door closing force after a predetermined time passes when the door is opened in a state of reducing the door closing force. Since the door closing force of the door closer is reduced in advance in a door closed state, when the person opens the door, the door can be opened by the light force in the state of reducing the door closing force without delaying in time.