There is provided a mobile communication system that can prevent a situation in which, although there is no occasion to receive packets for a mobile station, the reception processing is continued and useless power is undesirably consumed. The mobile communication system includes a base station that repeats a transmission period and a transmission halt period with a constant control cycle, and mobile station that repeats a reception period and a reception halt period with a constant control cycle (antenna, duplexer, reception unit, user data separation unit, packet transmission determination unit, reception period determination unit, packet reception determination unit, and signal synthesis unit). The mobile station alternately repeats the reception period and reception halt period, sends the reception result to the base station, and starts the reception period according to the start of the transmission period of the base station to receive packets. In case all the packets cannot be correctly received during the reception period, the reception period is extended by a predetermined period in the control cycle. Furthermore, in case all the packets can be correctly received during the reception period, the mobile station transfers to the reception halt period to halt the reception.