A mobile station 100 monitors, in Slotted mode, a Paging Channel Slot in a monitor cycle. The mobile station 100 includes: a user interface 53 which receives a PTT setting operation from a user for setting a PTT (Push to Talk) mode; a PTT communication control unit 51 which transmits an allocation request to the radio base station when the PTT setting operation is received; a slot cycle switching unit 52 which switches, when the PTT setting operation is received, the monitor cycle to a predetermined short cycle which is shorter than a cycle at the time of receiving the PTT setting operation; and a voice signal processing unit 40 which receives a voice packet after a PTT CALL is detected in a message transmitted from the radio base station to the mobile station, and reproduces a voice based on the voice packet.