An electronic apparatus comprising a radio transmitter is disclosed. In a computer system (1) having a radio transmission circuit (3) of a phase modulation type supplied with power from a power supply (4) of a switching type, the switching frequency of the power supply (4) is determined based on the comparison frequency for the sampling operation of a PLL circuit (10) of the radio transmitter, thereby removing the power noises generated from the switching regulator of the radio transmitter of a phase modulation type.