There are provided a driving control portion configured to output a closing command for bringing a contact to a closed state to a first driving portion, and also to output to the first driving portion an opening command for bringing the contact to an open state and the closing command in an alternate and repeated manner until the current runs through the contact; a number-of-retries obtaining portion configured to obtain, as a number of retries, the number of times that the driving control portion repeated the opening command and the closing command until the current runs through the contact after the driving control portion outputted the closing command to the first driving portion; and a usable period estimating portion configured to estimate a usable period from the present time of a first relay in accordance with the number of retries.