In a rainfall amount measurement apparatus, raindrop amount information corresponding to an attachment amount of raindrops attached to an outer wall surface of a windshield of the vehicle in a measurement period is acquired based on an output of a detector configured to generate an output corresponding to the attachment amount of raindrops. The raindrop amount information is used to set a wiping interval in a wiper wiping the raindrops attached to the outer wall surface. The measurement value of a rainfall amount per unit time is calculated based on the raindrop amount information, and outputted to an outside of the vehicle.