PURPOSE: To improve debug work efficiency by controlling a system so that a holding means holds data from one device to the other device when the clock of the other device stops.

CONSTITUTION: When a data request device 1 receives a clock stop request in the waiting state of input data 103, it is reported to a control circuit 5 that the clock is to be stopped by a clock report 104, and the clock is stopped at subsequent timing. When the control circuit 5 receives the report, it controls a buffer 4 by a buffer control signal 105 so that transfer data 101 transmitted from a data transmission device 2 is to be stored in response to a data transfer request 100. When data 101 is stored in the buffer 4, the effect is reported to a selection circuit 3 through a control signal 106. The selection circuit 3 switches control so that data 102 in the buffer 4 is selected as input data for the data request device.