The invention provides a relay device, a test method thereof and a computer readable medium for storing test program. The relay device for relaying transfer data to be transmitted between the devices has a plurality of testers. Each of the testers determines whether received transfer data is normal or not, and discards the transfer data that is determined abnormal. The relay device also has a counter that counts a number of transfer data discarded by each of the testers respectively, and a determiner that determines whether an operation of each tester is normal or not based on the number of discarded transfer data counted by the counter.