PURPOSE: To reduce number of components by inserting an isolator on the way of a data line through which a serial signal is sent so as to use only three isolators even when number of signal lines through which a parallel signal is outputted.

CONSTITUTION: When a 4-bit signal is inputted sequentially to a shift register 13a via an isolator 6 from a data line 10, the 4-bit signal is shifted at each input of a clock signal 11 and the 4-bit signal is held in the shift register 13a. When one-bit signal is outputted from the data line 10, the signal is shifted to next shift registers 13b, 13c. When data are set to the shift registers 13a∼13c, a 4-bit BCD signal is outputted from the shift registers 13a∼13c through signal lines 7a∼7l by using a strobe signal 12.