PURPOSE: To simplify the constitution of a synchronous word detector, by having the same synchronizing word for both the reference burst and the data burst with a time division multiplex communication system and using a burst discriminating code formed with a small number of bits during acquisition of synchronism.

CONSTITUTION: The same synchronous word (unique word) 4 is used for both reference and data burst data, and a burst discriminating code 5 consisting of two bits is added to the word 4. For the code 5, 11 and 00 are defined as the reference burst and the data burst respectively, for example. When the word 4 and the code 5 are detected during acquisition of synchronism, an estimation gate is opened after one frame. Furthermore, the estimation gate is opened after one frame if both word 4 and code 5 are detected in the same way. If the similar detections are carried out continuously with N frames within the estimation gate, it is decided that the reference burst has been caught in a correct way. Thereafter only the word 4 is detected within the estimation gate with no use of the code 5. The position of the data burst is decided on the basis of the position of the reference burst. Therefore the data burst can be correctly discriminated.