Power source apparatus with fuse-implemented over-current cut-off

The power source apparatus is provided with batteries 1 that supply power to a load; a current regulating circuit 2 that controls battery 1 current; a fuse 6 connected in series with the batteries 1; a first computation circuit 3 that computes a first allowable current that can flow through the batteries 1 based on at least one parameter including battery 1 specified current, temperature, voltage, and remaining capacity; and a second computation circuit 4 that computes a second allowable current that can flow through the fuse 6 without blowing the fuse 6 based on the time integral of current flow through the fuse 6. The current regulating circuit 2 controls the battery 1 current to a value lower than the first allowable current computed by the first computation circuit 3 and the second allowable current computed by the second computation circuit 4.