A first network device 71 and a second network device 72 transmits a test frame and its response frame therebetween. The first network device 71 acquires a test frame transmission start time, a response frame reception completion time, a test frame reception completion time, and a response frame transmission start time, and calculates, based on the times thus acquired, a PAUSE frame action delayed period that indicates a time period required for a PAUSE frame transmitted from the first network device 71 to actually act on the second network device 72, and sends from the first network device 71 to the second network device 72 a PAUSE frame in which a time period calculated based on the PAUSE frame action delayed period is set as a PAUSE period in order to prevent shortage of a receive buffer 244 in the first network device 71 from causing a loss of frames transmitted from the second network device 72.