To provide a portable ventilating operation machine capable of effectively executed while controlling the increase of weight or the increase of the size of an outward form to the minimum under such conditions as ventilating efficiency required for drastic reduction of sounds is ensured.

The said portable ventilating operation machine includes a motor and a ventilating section 30 consisting of a centrifugal front stage blower 31 rotated and driven with an output shaft of the said motor, the rear stage blower 32 and a joint ventilating passage 50 for connecting them. The joint ventilating passage 50 is so formed that its starting ends 51-54 are located on the circumferential side of a volute room 33A of the front stage blower 31 and, at the same time, its terminal end is located at an air suction port of the rear stage blower 32.