A base station in a mobile communication system includes a wireless communication unit for transmitting and receiving wireless signals with a user apparatus in a cell; a network communication unit for, in the case where the base station is connected to a communication network through a router, obtaining an address of the router, and periodically receiving time information from a time information server through the communication network; a memory unit for storing the address of the router and a current time indicated by the time information; and a control unit for, (1) in the case where a period during which the storing of the current time is stopped is equal to or greater than a threshold value, or (2) in the case where the stopped period is less than the threshold value and is equal to or greater than another threshold value, and an address just received from the router is different from the address stored in the memory unit, transmitting to the wireless communication unit a control signal for causing the wireless communication unit to stop the transmission of the wireless signal.