An in-vehicle radar apparatus includes a transmission and reception means which transmits a radar wave ahead of an own vehicle and receives a reflected wave corresponding to the radar wave from a target; a reception strength detection means which repeatedly detects reception strength of the reflected wave; a distance detection means which repeatedly detects a distance from the own vehicle to the target; an approximate expression calculation means which calculates an approximation expression expressing the reception strength using the distance as a variable from the reception strength repeatedly detected by the reception strength detection means and the distance repeatedly detected by the distance detection means; and a determination means which determines a height of the target from a road surface based on values of coefficients of the approximation expression.