ELECTRONICALLY DESIGNED TELEPHONE SET

PURPOSE:To attain excellent operation in a PB signal transmission circuit by changing a resistance value of one of two resistive elements deciding an output voltage in a constant voltage circuit in response to a control output signal of a PB transmission circuit. CONSTITUTION:When a pushbutton of the PB transmission circuit is depressed and a signal of a positive potential is incoming to a control signal terminal 12-2, a transistor 16-2 to be controlled is turned off. Thus, a voltage V between terminals 21 and 22 reaches a higher voltage V' by applying a resistance value R1 of a resistor 16-3. Thus, the excellent operation is attained by using the voltage to drive the PB transmission circuit.