PROBLEM TO BE SOLVED: To reduce the size of a device for measuring the characteristics of an optical transmission path.SOLUTION: A reception side conversion part 42 configures a reception part for receiving an optical signal from an optical transmission path 34 via a signal coupling and separating part 56. A reception difference measurement part 48 obtains a reception difference R21 indicating a difference between a time when a first optical signal has been received and a time when a second optical signal having wavelength different from the first optical signal has been received on the basis of a measurement result obtained by an information extraction part 44. A transmission difference measurement part 50 obtains a transmission difference T21 indicating a difference between a time when the first optical signal has been transmitted and a time when the second optical signal has been transmitted on the basis of information included in at least one of the first optical signal and the second optical signal. A di
