An in-vehicle radar device includes a transmission section, a reception section, an analysis section, an extraction section, a speed calculation section, a distance calculation section, and a folding detection section. The folding detection section detects occurrence of erroneous calculation of a distance, when reflection intensity at a frequency peak obtained by the extraction section is smaller than a preset intensity threshold for a distance calculated by the distance calculation section and a frequency width in a frequency spectrum calculated by the analysis section is smaller than a preset width threshold.