PURPOSE: To make it possible to rise to and fall down from the top of a revolving body easily and enhance a maintenance ability for an engine or the like by removably engaging a ladder with an engagement section installed to their rear part of a counter weight installed to an upper part revolving body.

CONSTITUTION: A ladder 11, when it is used, is turned upwardly, centering on the connection between an engagement member of the bottom of a counter weight 10 and the ladder 11 and erected on the rear side of the counter weight 10. Then, a link member on the upper end of the ladder 11 is engaged with the engagement member of the counter weight 10, thereby enabling the ladder 11 to be serviceable. After the ladder 11 is used, the link member is removed from the engagement member and the ladder 11 is adapted to fall down in the rear part, thereby turning the ladder to a horizontal state. Then, the ladder 11 is turned horizontally with the engagement member so that i may be housed in the bottom of the counter weight. After the ladder 11 is erected on the rear side of the counter weight, a pin 14 near the upper end of the ladder 11 on the outside surface on both sides is engaged with the engagement member so that the ladder 11 may be set to a serviceable state.