Optical axis adjustment jig and method of confirming optical axis of laser processing apparatus

There is provided an optical axis adjustment jig including a flat parallel-surface plate having an upper surface and a lower surface with reflective films disposed respectively thereon, and an image capturing unit disposed beneath the flat parallel-surface plate for capturing an image of a laser beam applied thereto. The flat parallel-surface plate is made of a material that is transmissive of a wavelength of the laser beam. The laser beam is applied through the flat parallel-surface plate to the image capturing unit. A tilt of the optical axis of the laser beam is detected on the basis of the shape of the beam spot of the laser beam whose image has been captured by the image capturing unit.