There is provided a unit capable of performing calculation of delay time between a measuring station and a station to be measured by using an echo request/response frame in any block and at any time in a manner being independent from time-synchronization. To a payload portion of an OAM (Operations, Administration and Maintenance) echo request/response frame to be used for an OAM testing are added “request transmitting time” being the time at which an OAM echo request has been transmitted from the measuring station and “response receiving time” being the time at which the measuring station has received an OAM response from the station to be measured. After termination of the testing, the OAM echo request/response frame stored in a data buffer is read at arbitrary time and the request transmitting time added to the frame and response receiving time are extracted to calculate delay time between the measuring station and the station to be measured.