A LDO and a switching regulator are connected in parallel with each other.
The power supply device selects and actuates either of the LDO or the
switching regulator in accordance with a switching signal from the
outside. When making the switch from the LDO to the switching regulator
so as to be actuated, the power supply device causes operation periods of
the LDO and the switching regulator to overlap each other. At least
during the period in which the operation periods overlap each other, the
power supply device makes current drive performance of a synchronous
rectification transistor of the switching regulator lower and makes the
same return to a normal state after the LDO stops its operation.