PARKING ASSISTANCE DEVICE

A parking assistance device of an embodiment includes: a captured image acquisition unit that acquires a captured image obtained by imaging a road surface around a vehicle; an end detection unit that detects an end of a ground object attached to the road surface included in a detection area set in the captured image; a position information calculation unit that calculates position information indicating a positional relationship of the end of the ground object detected with the vehicle; a boundary line determination unit that determines whether or not a ground object having the end is a boundary line that defines a parking slot for the vehicle; and a removal unit that determines whether or not a rear end of a ground object determined as the boundary line by the boundary line determination unit is included in a removal range, determines that a ground object determined as the boundary line is not the boundary line when the rear end is included in the removal range, and excludes the ground object from boundary lines, the removal range being a range that includes a front, an area on a side close to the vehicle, from a position including a vicinity of a front end of a boundary line having a front end on a side farthest from the vehicle before start of a parking operation among the boundary lines.