PURPOSE: To inform a worker of a turn mode without causing misunderstanding.

CONSTITUTION: When a slow turn and a super pivotal turn are switched by a switching lever, a change-over switch is put in an on or off state being interlocked with the switching lever 22 only at the time of the switching lever 22 selecting the slow turn, and a worker is informed of the selected turn mode by an acoustic device or a light emitting device or an informing device formed of both devices by the on or off state of a selecting switch 19 in correspondence with the on or off state of the change-over switch. The acoustic device informs with voice in correspondence with an operating position before the start of the turn and after the start of the oscillation to the left or right of an operating lever 18 for determining the turning direction, and the light emitting device informs the gentle turn mode by continuous or discontinuous lighting.