An inventive switching type dc-dc converter is adapted to set a protective reference current level lower for a decreased output voltage, and stop the switching control signal supplied to a switching transistor circuit when the detected current level exceeds the protective reference current level. In addition, in case where the output voltage declines due to, for example, a circuit failure such as short-circuiting, the switching period of the switching transistor circuit is extended. Thus, the switching type dc-dc converter is provided with a fold-back current limiting type protection characteristic through reduction of the protective reference current level and extension of the switching period of cycle.