To enable the highly efficient mixture of two kinds of fluids in a fluid mixing device suitable for an ozone water supply device and the like for supplying ozone water while maintaining its high concentration.

The fluid mixing device comprises a first mixer 11 for mixing a first fluid and a second fluid by jetting the second fluid from an injector pipe 41 opening inside a venturi tube into the first fluid accelerated in a small-diameter part 67 in the venturi tube, a passage 19 for rectification made of a pipe having an almost constant thickness to rectify the flow direction of the whole mixed liquid by idle running of the mixed liquid of the first and second fluids discharged from the first mixer 11 by a prescribed distance, and a second mixer 12 made of a pipe having an expanded diameter part 45 expanding the internal diameter so that the cross section area of the passage becomes larger than that of the passage 19 for rectification, and disposing an almost conical block 46 in the expanded diameter part 45, of which the tip of the cone is oriented toward the upstream side and of which the bottom is oriented toward the downstream side, and of which the peripheral surface has a stepwise unevenness having surfaces almost vertical to the flow direction and colliding with the mixed liquid.