A conventional carrier detecting circuit which generates a carrier detection level by integral action based on a reception signal and detects using the carrier detection level whether a carrier exists is arranged to charge and discharge in the following manner, an integration capacitor in an integrator that performs the integral action. Namely, the integration capacitor is (i) either charged or discharged in accordance with a result of the discrimination of the reception signal at the carrier detection level, or (ii) charged in accordance with the result of the discrimination while the integration capacitor is constantly discharged at a constant level. In contrast, a carrier detecting circuit of the present invention is arranged so that the integration capacitor is both charged and discharged constantly at a level that varies in accordance with the result of the discrimination. In other words, the integration capacitor is charged and discharged using a difference current between a current charged from a charging circuit and a current discharged to a discharging circuit. With this, it is possible to reduce the chip area without causing problems due to the reduction of the currents flowing through the transistors.