A user apparatus that transmits and receives a discovery signal, including: collision detection means that detects a collision in a received discovery signal; collision notification means that, when a collision of a received discovery signal is detected by the collision detection means, transmits collision information indicating that a collision occurs in the received discovery signal; collision information reception means that receives collision information; and collision determination means that determines whether a collision occurs in a transmitted discovery signal transmitted by the user apparatus based on the collision information received by the collision information reception means.