A mixing element, which is produced at low cost, has high mixture agitation effectiveness, and is easily made large, and a static fluid mixer using the mixing element are provided. Further, a gas-liquid treatment apparatus with high treatment ability is provided. A mixing element 1 includes: a cylindrical passage tube 2 trough which fluid flows; a plurality of spiral rightward rotation type first blades 3 formed of a perforated object, which are provided in the passage tube 2; a first inner cylindrical tube 5 shaped like a cylinder and disposed inside the blades 3; a plurality of spiral rightward rotation type blades 6 provided in the inner cylindrical tube 5; and an opening 9 formed in the axial center portion of the blades 6. A static fluid mixer is formed by using at least one mixing, element 1 mentioned above.