A flux control apparatus includes an outlet pressure detector for detecting an outlet pressure of a fluid at an outlet of a fluid flow apparatus driven by a drive source for feeding the fluid from an inlet of the fluid flow apparatus and letting the fluid flow out from the outlet of the fluid flow apparatus, a drive amount detector for detecting an amount of drive of the drive source, an estimated flux-calculating apparatus for calculating a flux of the fluid flowing from the fluid flow apparatus as an estimated flux on the basis of the pressure of the fluid and the amount of drive, a control amount-calculating apparatus for calculating an amount of control for the fluid flow apparatus on the basis of the estimated flux and a target flux, and a control apparatus for controlling the drive source on the basis of the amount of control.