A voltage raising device that provisionally maintains an operation and function when there is an abnormality provided. If a battery voltage drops when an engine is restarted after an idle stop, the voltage raising device raises the output voltage to a target voltage by using a voltage detecting circuit and a current detecting circuit. If an overcurrent determining circuit detects overcurrent, a switching control circuit reduces the target voltage to perform a control. If overvoltage is output, for example, due to an increased target voltage caused by an internal setting deviation resulting from a failure, an overvoltage detecting circuit outputs a prohibition signal ENV to stop the switching operation. However, as long as the output voltage is not overvoltage, the voltage raising operation is allowed. Therefore, the possibility that the engine can be started at least once without a problem is increased.