PURPOSE: To always grasp a line state under communication without adding any optional information to transmitting data concerning the communicating state grasping system for a line between terminals.

CONSTITUTION: The line for grasping the state is formed between the terminals, a transmitting part 1 of the terminal is provided with specified pattern generating parts 1a and 1b, and a receiving part 2 is provided with a specified pattern generating part 2c for generating the similar specified pattern to the transmitting part 1, timing control part 2b for controlling the timing of the specified pattern generating part 2c corresponding to a received signal, and specified pattern comparing part 2d. When the specified pattern is transmitted from the transmitting part 1 of one terminal to the line 3 for grasping the state and the signal of the specified pattern is received from the line 3 by the receiving part 2 of the other terminal, the received specified pattern is compared with the output of the specified pattern generating part 2c, of which the timing is controlled, by the specified pattern comparing part 2d and based on the compared result, the communicating state is decided.