PURPOSE: To test whether or not a desired characteristic is obtained by confirming whether or not each circuit normally operates in accordance with each parameter, whose frame synchronism is set by using the frame synchronizing characteristic when data are divided in the unit of frame.

CONSTITUTION: At a unique-word noise generator 1, the position of a unique word is recognized based the frame timing from a unique word inserter 11 and a previously set noise pattern is produced at the position of the unique word. After a unique word detector 16 and synchronism protector 17 perform detection and synchronism protection on the unique word, into which noises are inserted, a synchronized state signal is inputted to a synchronized state measuring instrument 2 and synchronism or asynchronism is detected from the signal. After detection, the time of the synchronism or asynchronis is measured. When the actually measured value is compared with a theoretical value, whether or not each circuit normally operates can be confirmed.