To enable mainly a fixing and a removal of a front surface hood against a hood main body to be easily carried out without requiring any troublesome work of sequential fixing and removal of fixing component parts and at the same time enable a possibility of losing the fixing component parts to be eliminated.

A front surface hood 23 is fixed to a hood main body 22 through a sliding engagement between a first engaging protrusion 31 arranged at a hood main body 22 and an engaging hole formed at the front surface hood 23 as well as another engagement attained by a resiliency of the spring 36 between a spring 36 arranged at the hood main body 22 and a second engaging protrusion 43 arranged at the front surface hood 23. The spring 36 is operated from this state to be flexed, thereby the engagement between the spring 36 and the second engaging protrusion 43 is released and after this operation the engagement between the first engaging protrusion 31 and the engaging hole is released to enable the front surface hood 23 to be removed from the hood main body 22.