To set all TS(time slots) included in a multiplexed signal to each card optionally while employing terminal station interface cards and card slots whose number of pieces is less than the number of sets of multiplexity.

In this multiplexer, a multiplex cards including a multiplexer 156 for multiplexing/demultiplexing and eight terminal station interface cards 152a-152h less than the number of sets of multiplexity (24) are interconnected via buses. Then each of the terminal station interface cards 152a-152h is provided with a means to set HG and TS shared by each card. Thus, each of the terminal station interface cards 152a-152h sets the HG and TS to have provision for a desired TS among 24 sets of TS. Thus, an optional TS is set to each card while reducing the cost.