To obtain a power supply apparatus and an overcurrent alarm apparatus that assures to issue the warning for an overcurrent without operation of an over-current shut-off breaker at the time of loading of a new power load.

A power supply apparatus 500 supplies a power to each power distributing paths 102A to 102C via an overcurrent shut-off breaker 60 from a power feeding line 100. When a new power load 201D is connected to a distribution path 102C, connection is not immediately established, but an additional current detecting part 150 detects an additional current x1 required by a power load 201D and then communicates it to a remaining current detecting part 160. The remaining current detecting part 160 determines whether a residual current value (a1-y1) that is equal to the difference between the present current value y1 and the regulated current value a1 of the overcurrent shut-off breaker 60 is equal to or larger than the additional current value x1. When these are equal, a power is supplied, but when these are not equal, overcurrent alarms 158A/158B are issued. When an overcurrent shut-off breaker is also provided in the distribution paths 102A to 102C, similar determination is performed to execute the connection or alarming operation. An additional current detection part 150 and a residual current detecting part 160 are also provided as an overcurrent alarm apparatus 600.