An arc detecting device includes a detector for acquiring time series data concerning a characteristic quantity, such as a voltage or a current in a circuit, targeted for detecting an arc; a basic data generator for generating basic data made of a plurality of frequency components, through frequency analysis from the acquired time series data; a data processor for statistically processing the generated basic data, thereby converting the basic data to an evaluation value highly correlative to an occurrence of the arc; and an arc judging unit for judging the occurrence of the arc, if the evaluation value exceeds a predetermined arc judgment threshold value. In this manner, the arc detecting device that is capable of effectively detecting the arc in a direct-current power supply circuit is provided.