To take measures against cold climates without providing an outside air heater.

There is provided an air conditioning apparatus 40 for a construction machine, which is arranged in a cabin 9, and includes a heater box 42 having a fan heater 41 built therein, an air intake duct 44 for sucking air into the heater box 42 by using suction force of fans of the fan heater 41, and an exhaust port 45 for heating the air within the heater box 42 to a set temperature by a heating body of the fan heater 41 and then blowing the heated air into the cabin 9 by using blow-off force of the fan. The air intake duct 44 is comprised of a damper which can switch between at least two intake modes out of three, i.e., an inside air intake mode in which air only inside the cabin 9 is sucked to the heater box 42, an outside air intake mode in which only outside air is sucked, and a mixed air intake mode in which air both inside and outside the cabin is sucked.