PURPOSE: To improve the working efficiency and the space efficiency by forming an on-board bore siting device of a reflecting plate provided at a bore siting reference face, and an optical head part, provided on a bore siting mount, having a visible light source, a half mirror and a screen.

CONSTITUTION: An on-board bore siting device is formed of a reflecting plate 1 provided at the on-board bore siting reference face 5 of an aircraft and an optical head part 3 provided at the bore siting mount 4 of the aircraft. A visible light source 6 is formed of one with good convergence such as He-Ne laser, and the light emitted from the visible light source 6 is made into parallel light by an expander 7, passes a pin hole 8, penetrates a half mirror 9, and is reflected by the reflecting plate 1. This reflected light is reflected by the half mirror 9 so as to form a spot on the face of a screen 10. This spot is observed by an ocular 11, and the position and attitude of the bore siting mount 4 are adjusted so as to place the spot into the specified position to perform bore siting.