The invention discloses transmit power control that easily controls transmit power for transmitting a signal to a mobile terminal so that the transmit power has an optimal value. When there is a succession of transmit power control information transmitted from a mobile terminal to the radio base station, that includes an instruction to raise transmit power, during a period from when a calculated total transmit power, based on power information of a multiple signal that is obtained by multiplexing signals transmitted by each mobile terminal, exceeds a preliminarily set power threshold to when the total transmit power falls below the preliminarily set power threshold, the transmit power control information is converted to transmit power control information that includes an instruction to maintain transmit power at a constant level. The transmit power is controlled based on the converted transmit power control information. The signal is transmitted to the mobile terminal by use of the controlled transmit power.