An ejector having an ejector body integrally formed with a nozzle having inlet and outlet ends, a diffuser having inlet and outlet ends and a suction passage defining a suction port between the outlet end of the nozzle and the inlet end of the diffuser. The nozzle and diffuser define fluid passages having a rectangular cross section or a circular cross section in which the narrowest portion of the fluid passage of the nozzle defines a throat. The diffuser has a diverging portion which diverges to have a divergence angle of 5-10 degrees in case of a two dimensional ejector or 3.5-6.5 degrees in case of a three dimensional ejector.