An upper revolving structure is provided with a revolving frame, a floor member, and a cab box. On this, an indoor unit for an air conditioner is provided on the floor member, and an outdoor air inlet port is provided by being opened to the outside of the cab box. An outdoor air duct is provided for supplying outdoor air introduced through the outdoor air inlet port toward the indoor unit. In this duct, an intermediate portion is arranged at a high position on the side of an operator's seat, and on this intermediate portion, a filter accommodating portion is provided by being opened into the cab box. In the filter accommodating portion, an outdoor air filter for trapping dusts in the outdoor air flowing through the outdoor air duct is accommodated capable of being attached and removed.