The invention includes an output circuit that outputs an operation signal to a direct current breaker that interrupts a direct current main circuit, and a processor that samples, at predetermined time intervals, digital data wherein a value detected by a direct current transformer that detects a current of the direct current main circuit is measured as an input current, calculates a computed measurement value to be output to a display circuit, and outputs control information for executing a protection process using measurement value sampling data obtained by the sampling to the output circuit, and executes a protection process of the direct current main circuit at every sampling.