To provide a power source position alarm device and a method capable of preventing trouble that a door is reopened and operation is re-started after the door is closed by outputting an alarm before getting off of an occupant.

When a shift position is not operated to P range at stopping of an engine, a shift position P range returning forgetting alarm is outputted. The power source position alarm is successively outputted until the power source position is transformed to the power source position where steering lock is executed even when the shift position is operated to P range during the alarm.