Mismatch detecting method, detecting device, and recording medium

A mismatch detecting method includes: specifying a configuration of test data in accordance with a condition in which a time when a first packet out of a plurality of packets included in the test data caused to make a round trip through a transmission path including a plurality of sections is transmitted in one section out of the plural sections in an inbound path and a time when a second packet out of the plural packets is transmitted in the one section in an outbound path overlap with each other; transmitting the test data to the transmission path in accordance with the configuration specified by the specifying; and determining a mismatch of a transmission system within the transmission path, based on a loss situation of the test data returning from the transmission path after the transmitting.