Operation mechanism of a working machine includes a main clutch lever pivotably provided on an operating handle, and a pivot member operable in interlocked relation to pivoting operation of the main clutch lever. The pivot member pivots about a pivot point differing in position from a pivot point of the main clutch lever. When fully pulled by pivoting operation of the main clutch lever, the cable member is located nearest to the pivot point of the pivot member, so that force reverse-pivoting the pivot member is reduced.