comprises a secondary exit pipe 63 generally coaxial with the discharge conduit 4 and at least one connecting pipe 62 each of which connecting a secondary air inlet 61 to the secondary exit pipe 63 the secondary air b inhaled through the secondary air inlet 61 is isolated from the primary air a inhaled through the primary air intake conduit 1 by the secondary air intake pipeline 6 until it reaches the end of the secondary exit pipe 63 where the later communicates into the discharge conduit 4 and thus the secondary air b mixes with the primary air a at the beginning of the compression operation the primary air a entering the air pump if first compressed in the multi stage centrifugal compressing section 2 in the same way as described above with respect to a conventional air pump and then accelerated within the discharge conduit 4 having a profile similar to a nozzle so as to produce a lower pressure in the vicinity of the end portion of the secondary exit pipe 63 the produced lower pressure in turn inhales secondary air b from the outside of the air pump through the secondary air intake pipeline 6 so that the secondary air b together with the primary air a may be pumped into an inflatable article connected to the discharge conduit 4 due to the addition of extra secondary air b to the total air supply rather than merely the primary air a as in the case of a conventional air pump this air pump can inflate an inflatable article in a more speedy manner as compared with a conventional multi stage centrifugal compressor or air pump described above and shown in fig1 to 3 fig5 and 6 show the construction of an air pump in accordance with.