PURPOSE: To quickly and easily find out an error in a word identification code by detecting the error automatically when an error takes place in the word identification code.

CONSTITUTION: A detection circuit 100 is connected to the error check circuit in order to check an error in a word identification code WI and generates an error check signal DET when the error in the word identification code WI is detected. Moreover, the detection circuit 100 is connected to a measurement device 200 to observe a waveform of the word identification code WI by using an error check signal DET as a trigger. Thus, when an error takes place in the word identification code WI, the detection circuit 100 generates an H level error check signal DRT and it is used as a trigger for the measurement device 200 to observe the waveform of the word identification code WI.