A target object information estimating device embodied by an electronically agile radar sensor is mounted in a moving vehicle. The device has a unit outputting a radar wave every measuring period, receiving radar waves reflected from a target object through different transmission paths and calculating a distance to the object in each measuring period to detect the object, a unit tracking the object in a tracking term of measuring periods, a unit setting the distance changed with time as a null distance each time electric power of the received waves is reduced to a minimal value, and a unit producing an actual pattern of null points corresponding to the null distances, collating the actual pattern with modeled patterns corresponding to various heights and estimates the height of the object from the collation result as information about the object.