Abstract: A measurement method includes a step of measuring an object to be measured and a reference object by a first measurement unit and a second measurement unit. The first measurement unit has a first displacement meter and a second displacement meter that face each other in a first direction and measure the distance from the object to be measured. The second measurement unit has a third displacement meter and a fourth displacement meter that face each other in the first direction and measure the distance from the reference object. A frame-like supporting member includes a first frame portion supporting the first displacement meter and the third displacement meter, a second frame portion supporting the second displacement meter and the fourth displacement meter, and a third frame portion and a fourth frame portion that connect both end portions of the first frame portion and the second frame portion to each other.

Abstract: An optical axis adjustment jig includes a main unit portion that is configured to be disposed between a pair of head units, and is fashioned in a flat plate shape. The main unit portion includes a reference portion for adjusting a distance between the head units, and an inclination of an optical axis of each of the head units, and a screen portion for aligning the optical axes of the head units. The reference portion and the screen portion are disposed arrayed in a direction orthogonal to a thickness direction of the main unit portion.