An object detector includes: an acquiring unit that acquires an oscillation signal corresponding to an oscillation of a microphone, the microphone transmitting a transmission wave, which is an ultrasonic wave, on a basis of a driving signal, and being caused to oscillate by a reflected wave generated as a result of the transmission wave being reflected from an object; a fall identifying unit that identifies a fall time point of a first drop from a value more than a threshold to the threshold or less after termination of the driving signal; a rise estimating unit that estimates a rise-in-reverberation time point of the reflected wave, the rise-in-reverberation time point being before the fall time point and after a time point of start of the driving signal; and a distance determining unit that determines a distance to the object on a basis of the rise-in-reverberation time point.