An obstacle detection apparatus includes: a transceiver transmitting a transmission wave and receiving an ultrasonic wave; a transmission controller; a receiver circuit detecting a signal level of a receiving wave; a distance calculator sequentially calculating a distance to an object reflecting the transmission wave; a memory storing the distance to the object; an obstacle determination device determining whether the object is an obstacle; and a reception level monitoring device monitoring the signal level of the receiving wave before the transmission wave being transmitted. When the signal level exceeds a predetermined threshold, the obstacle determination device sets a first number of determination data elements to an increased number of determinations for a predetermined period to be used for determining whether the object is the obstacle, as being larger than a second number of determination data elements used when the signal level does not exceed the predetermined threshold.