To provide a pseudo-carrier transmission system that can monitor channel quality without causing erroneous detection of a pseudo-carrier system.

A selection circuit 12 of its own station side outputs data from its own station terminal 3, when a control signal is set and outputs a PN pattern generated by a PN pattern generating circuit 11, when the control signal is reset. A PN pattern detection circuit 21 of an opposite station side detects the PN pattern from the data of its own station side and provides the output of a fact that the control signal is reset, when the PN pattern is detected and that the control signal is set, when no PN pattern is detected. An AND circuit 22 transmits the data of its own station to an opposite station terminal 4, when the control signal is set and stops the transmission of the data to the opposite station terminal 4, when the control signal is reset. An AND circuit 23 inhibits the result of collation of the PN pattern, when the control signal is set and outputs the result as it is when the control signal is reset.