To make a safety mechanism operable even if something abnormal occurs while operation of a load is stopped.

A power supply unit includes a battery block 9 formed by connecting a plurality of secondary battery cells 1 in series or in parallel, abnormality determining means for determining abnormality of the battery block 9, a power supply case 70 for housing the battery block 9 and the abnormality determining means, abnormality detecting means for detecting abnormality that causes a physical change to the battery block 9 and sending out a detection signal; and output connecting means for switching ON/OFF of the connected state of the output of the battery block 9 and the input of an apparatus to be driven. The abnormality detecting means can detect abnormality even if the output connecting means is in an OFF state. In response to the abnormality detecting means detecting abnormality and sending out a detection signal in the OFF state of the output connecting means, the abnormality determining means determines whether or not the battery block 9 is abnormal, and when it is determined to be abnormal, restricts switching of the output connecting means to the ON state.