To easily and surely switch a connection line.

In a line switch device 4, when an instruction to switch the connection line is received from a monitor center, a port state monitor part 13 detects a signal reaching an auxiliary side port 11 from the monitor center and reports it to a switch control part 14. The switch control part 14 reads a time difference between timing to switch the state (open/close) of the auxiliary side port 11 and timing to switch the connection destination of a line connection switch part 12 from the signal received from the port state monitor part 13 and sets it to a time counting part 22. The switch control part 14 switches the state (open/close) of the auxiliary side port 11 or connection destination of the line connection switch part 12 at the switch timing reported from the monitor center. The time counting part 22 counts the time and can switch the state (open/close) of the auxiliary side port 11 and the connection destination of the line connection switch part 12 at the prescribed switch timing.