middle part of the revolving frame 3 a in front of the engine cover 13 on the seat base 21 the operator 39 s seat 5 is placed and inside the seat base 21 an air conditioner 20 is contained on upper right and left sides of the seat base 21 lever controlling devices 22 r and 22 l for controlling a boom cylinder and bucket cylinder of the excavator unit 4 and a revolving motor for the machine base 3 and the like are arranged with being distributed right and left across the operator 39 s seat 5 on an upper surface of the revolving frame 3 a in front of the seat base 21 a floor step 23 is detachably provided in front of the floor step 23 a front floor plate 19 is provided in such a way as to vertically penetrate through the front floor plate 19 a traveling lever controlling device 24 for controlling hydraulic motors of the traveling units 2 and the like is arranged in the front part of the revolving frame 3 a and also a traveling accelerator pedal a swing pedal for operating a swing cylinder of the excavator unit 4 and the like are arranged upward from a right front of the seat base 21 an air duct 25 is protruded the air duct 25 is communicatively connected to the air conditioner 20 a plurality of air blowing ports 25 a for blowing cooling air to a windshield operator 39 s seat 5 and the like in the cabin 7 is formed and on a back side of an upper part of the air duct 25 a meter panel 26 is provided the air duct 25 and the meter panel 26 constitute an operation.