According to an embodiment, a distance measuring device is a signal processing device that performs processing on time-series luminance signals of each of frames acquired on the basis of reflected lights of laser lights irradiated in order in a plurality of predetermined directions for each of the frames. The distance measuring device includes a storage circuit and a selection circuit. The storage circuit stores information concerning a distance value obtained on the basis of a time-series luminance signal of a preceding frame. The selection circuit selects a peak based on the distance value as a candidate of the distance value out of peaks in the time-series luminance signal in a present frame.