1. A target detection apparatus, comprising: a first target detection section which detects a target which exists ahead of a vehicle and has a height sufficient to strike against the vehicle; a second target detection section which detects the target in an area different from an area in which the target is detected by the first target detection section; and a reliability degree setting section which sets a target reliability degree indicating probability that the target exists, wherein when the target is detected only by the first target detection section or the second target detection section, and after the target is detected by both the first target detection section and the second target detection section, the reliability setting section sets the target reliability degree based on an overlap detection time which is a period of time during which both the first target detection section and the second target detection section continuously detect the target.