A backdoor opening and closing apparatus includes an operation input detection portion detecting an operation input for operating a backdoor in response to a detection signal sent from a sensor configured to include a detection area at a lateral rear portion of a vehicle, an operation control portion operating the backdoor in response to the operation input, a passenger determination portion determining whether an authorized passenger is positioned within a common area where a lateral portion determination area and a rear portion determination area overlap with each other, and an allowance determination portion allowing a predetermined operation of the backdoor in response to the operation input in a case where the passenger determination portion determines that the authorized passenger is positioned within the common area (αx).