PURPOSE: To attain quick countermeasure even if a new PB signal is requested, by using a microprocessor for the generation 10 of a PB signal so as to read out an ROM, reducing considerably an ROM IC part and generating a digital PB signal in an economic way.

CONSTITUTION: In the figure, 20 is a section interacting whith an exchange. Data generating the PB signal are stored in a memory (ROM) in a PCM code built in the microprocessor 21, 22. The data corresponding to a cell tone, a busy tone and a dial tone are stored in the PCM code in the built-in memory of the microprocessor 23, DO is an output terminal of a parallel PCM coding data and INT is a terminal receiving an interruption command. A register in the microprocessor is used as a presettable counter and receives a periodic readout start command (interruption signal) from a control section, decrements a value of register with a program one by one so as to form an address to the ROM, and the data of the PB signal stored in the ROM is read out as the PCM code and controlled.