According to an aspect of the present invention, at least parts or all of the windows for tarry lamps are located in the outside of the front cover by constructing the front cover portion between the top face and left-hand side face of the front cover, and the front cover portion between the top face and right-hand side face of the front cover as the inclined planes respectively. That is, since the windows for tarry lamps are not covered by the front cover as conventional ones, visibility from the external improves.