PURPOSE: To secure function, to simplify a circuit constitution, and to reduce power consumption by converting a clock pulse generated by frequency-dividing a two-frequency signal by the output of a decoder, and performing oscillation.

CONSTITUTION: A dial signal passed through a signal control part 16 is decoded by low-group and high-group frequency decoders 15 and 16 and variable frequency dividers 17 and 18 provided corresponding to the decoder 15 and 16 divide the frequency of clock pulses according to decoder outputs. Serial-parallel converting circuits 19 and 20 provided corresponding to the frequency dividers 17 and 18 convert the outputs of the frequency dividers 17 and 18 into analog signals, which are mixed by a mixing circuit 23, whose output is set to a specific level by a level setting circuit 24 and sent out. Said circuits constitute a two-frequency signal oscillator 10, which is provided to a digital telephone device. Consequently, a selection signal corresponds to a two-frequency signal accurately and this constitution requires only one clock pulse generating circuit to reduce the power consumption.