To provide a cover structure of a grinding wheel spindle for covering the grinding wheel spindle with a grinding wheel spindle cover ensuring good work efficiency in replacing a grinding wheel.

The cover structure of the grinding wheel spindle is provided with the grinding wheel spindle 70 composed of a first grinding wheel spindle 71 and a second grinding wheel spindle 72 axially separable from each other, to attach/detach the grinding wheel T thereto through a clearance between the first grinding wheel spindle 71 and second grinding wheel spindle 72 in the separated state; an assembly object to which the grinding wheel spindle 70 is assembled; a first bearing for supporting the first grinding wheel spindle 71 to the assembly object; a second bearing 62b for supporting the second grinding wheel spindle 72 in an axially movable manner to the assembly object; and the grinding wheel spindle cover 90 composed of a plurality of radially separable cover bodies (a first cover body 91 and a second cover body 92) and mounted to a portion between the grinding wheel T and the second bearing 62b at the second grinding wheel spindle 72 from the radial direction to cover the outer peripheral surface of the second grinding wheel spindle 72.