A passing determination device acquires a first captured image obtained by repeatedly capturing an image of a region including a passing determination position of a trailer from a front of the trailer in a traveling direction of the trailer, and detects the trailer from the first captured image. Further, the passing determination device includes a processor configured to determine that the trailer detected from the first captured image captured at a first time passes through the passing determination position when the trailer is detected from the first captured image captured at the first time and the trailer is not detected from the first captured image captured within a first time period from the first time.