In an in-vehicle target detecting device, a captured image which is an image capturing an area ahead of the own vehicle is acquired at a predetermined measurement cycle. Radio waves are transmitted and received. Positional information indicating at least an orientation and a distance of at least one target candidate in relation to the own vehicle is acquired. The target candidate reflects radio waves. Image recognition is performed to detect a detection object by searching a predetermined image search area in the captured image. At least an image detection position of the detection object in the captured image is stored. The image search area is set, based on an image-plane measurement position corresponding to a measurement position in the captured image. The measurement position is a position in three-dimensional space of the target candidate indicated by the positional information acquired at a timing at which the captured image is acquired.