The operator's cab 8 is provided with a floor frame 10 having an opening for maintenance 20 located at a floor base 10a and a lid body 23 for closing the opening for maintenance 20. The lid body 23 includes an upper inspection cover 22 and a lower inspection cover 21 which are aligned in a vertical direction with spacing so as to be attachable and detachable relative to the opening for maintenance 20. Disposed in a space between the upper inspection cover 22 and the lower inspection cover 21 is a floor duct 30 that can be disassembled and is provided for circulating supply air sent from an air conditioner 27.