An eye point measuring device configured to measure a three-dimensional position of an eye of an occupant sitting on a seat device of a vehicle by using a monocular camera positioned at a fixed position, wherein the eye point measuring device calculates the three-dimensional position of the eye of the occupant based on: a position change amount between a position of the eye of the occupant before the adjustment of the position of the seat device and a position of the eye of the occupant after the adjustment of the position of the seat device in a superimposed image in which an initial image and an after-adjustment image are superimposed on each other; a component, parallel to the superimposed image, of a movement amount of the seat device from a position before the adjustment to a position after the adjustment; and an angle of view of the monocular camera.