A user terminal according to an embodiment is a user terminal configured to exist in a first cell in a mobile communication system that supports a D2D proximity service between the user terminal configured to exist in the first cell and a user terminal configured to exist in a second cell. The user terminal comprises: a controller configured to measure a timing difference between a timing of a signal received from the first cell and a timing of a signal received from the second cell; and a transmitter configured to notify a base station configured to manage the first cell, of the timing difference.