PURPOSE: To secure transmission quality by measuring the line quality of a lamp line when the lamp line is used as a transmission line for data transmission.

CONSTITUTION: A test data transmission part 20 inputs test data from a test data generator 2 to a multiplier 5, performs spread spectrum processing by spread codes from a spread code series generator 3, and sends the data out to the lamp line 40. A reception part 30 inversely spreads the received data by a multiplier 12, makes a symbol comparison with transmission-side data by a comparing and calculating circuit 15, and calculates error symbols to measure the transmission quality of the line.