A working machine comprising a machine body and a structure for mounting a mountable/dismountable component on the machine body, comprising: a plurality of locking sections (38a, 62) provided on the machine body for locking the mountable/dismountable component; and a plurality of engagement sections (71, 75) provided on the mountable/dismountable component and engageable by respective ones of the plurality of locking sections (38a, 62), the plurality of locking sections including: a movable locking section capable of sliding the mountable/dismountable component to a predetermined mounting position on the machine body while locking a first engagement section of the engagement sections; and a fixed locking section constructed to lock a second engagement section, different from the first engagement section, of the engagement sections of the mountable/dismountable component in the predetermined mounting position, characterized in that the second engagement section is provided on each of left and right sides of the mountable/dismountable component as left and right second engagement sections extending outwardly away from each other in a width direction of the mountable/dismountable component, and wherein the mountable/dismountable component further includes left and right taper sections formed on left and right side portions of the mountable/dismountable component and located inwardly, in the width direction of the mountable/dismountable component, of corresponding ones of the second engagement sections, each of the left and right taper sections tapering continuously to the corresponding second engagement section. a plurality of locking sections (38a, 62) provided on the machine body for locking the mountable/dismountable component; and a plurality of engagement sections (71, 75) provided on the mountable/dismountable component and engageable by respective ones of the plurality of locking sections (38a, 62), the plurality of locking sections including: a movable locking section capable of sliding the mountable/dismountable component to a predetermined mounting position on the machine body while locking a first engagement section of the engagement sections; and a fixed locking section constructed to lock a second engagement section, different from the first engagement section, of the engagement sections of the mountable/dismountable component in the predetermined mounting position, a movable locking section capable of sliding the mountable/dismountable component to a predetermined mounting position on the machine body while locking a first engagement section of the engagement sections; and a fixed locking section constructed to lock a second engagement section, different from the first engagement section, of the engagement sections of the mountable/dismountable component in the predetermined mounting position, the second engagement section is provided on each of left and right sides of the mountable/dismountable component as left and right second engagement sections extending outwardly away from each other in a width direction of the mountable/dismountable component, and wherein the mountable/dismountable component further includes left and right taper sections formed on left and right side portions of the mountable/dismountable component and located inwardly, in the width direction of the mountable/dismountable component, of corresponding ones of the second engagement sections, each of the left and right taper sections tapering continuously to the corresponding second engagement section.