1. A laser welding inspection device comprising: an imaging device which receives reflected laser light that is the irradiation of laser light reflected by a welding portion and which images the welding portion by means of the reflected laser light received; a first lens unit and a second lens unit that are arranged in this order and placed between the welding portion and the imaging device, the first and the second lens units passing at least the reflected laser light between the irradiation and the reflected laser light of the welding portion; and a protection glass that is placed between the first lens unit and the welding portion so as to protect the first and the second lens unit, the laser welding inspection device inspecting welding quality using a welding portion image acquired from the imaging of the imaging device, a diaphragm between the imaging device and the protection glass that limits a direction range of a light beam incident from the protection glass; wherein a first image formation point corresponding to the welding portion is placed between the first and second lens units; and a protection glass-intended image formation point corresponding to the protection glass is placed between the first image formation point and the second lens unit, whereby the imaging device is not adapted to pick up the protection glass-intended image formation point so as to diffuse images of dirt on the protection glass.