Unwanted electromagnetic waves are eliminated in a frequency output circuit comprising an open-collector output terminal whereby radio noise can be reduced. A frequency output circuit 10 comprises an open-collector transistor Q4 with an open-collector output terminal connected to a pull-up resistor Rf connected to an external power supply Vex. A current limiting circuit 16 limits a current through the output terminal such that a high potential and a low potential of the output waveform of a frequency signal outputted by an output circuit 12 are smoothly switched. The current limiting circuit 16 is formed by a differential pair circuit of transistors Q1 and Q2 each with a resistor provided in the emitter thereof, and a current mirror circuit comprising an open-collector transistor, for example.