PURPOSE: To easily and efficiently execute the switch monitoring of a time division multiple calling channel by being equipped with plural coincidence circuits, channel memories and gate circuits and obtaining the AND of an address coincidence output and read-out calling data.

CONSTITUTION: As data necessary to check calling data, the data X0, X1, X2... of read-out calling data 59 are read out from the output terminal 0 of a channel memory 31. To make the data effective, an address coincidence pulse is inputted into an input terminal I2 of a gate circuit 45. By the timing of this pulse, an address coincidence output pulse 62 is latched in a coincidence circuit 44. This timing is equivalent to respective parts 63-0 and 63-1... respectively corresponding to a test address 55 to be inputted into the input terminal I1 and I2 of a coincidence circuit 36 and a channel X of a read-out calling data 61. In the circuit 45, pulses 62 and 63 are ANDed, and a test result output pulse 64 is outputted from a terminal 46.