A range finder 100 includes a transmission optical system 20 that transmits signal light toward a target object, a detection optical system 30 that has a different optical axis from that of the transmission optical system and detects the signal light reflected from the target object, and a photodetector 12 that is disposed on an imaging surface of the detection optical system. A distance to the target object is measured on the basis of a time difference between a transmission time and a detection time of the signal light. The detection optical system 30 includes a variable focal length optical system 14 that makes the focal length of the detection optical system variable, thereby providing a range finder capable of measuring a distance to a target object that locates from further away to nearer by using a photodetector having the same size.