The present invention provides a protein capable of binding to a female sex hormone, which protein is supplemented with useful properties for measuring, quantifying and concentrating female sex hormones, such as high sensitivity, low cross-reactivity, unlikelihood of being influenced by interfering substances, and unlikelihood of being influenced by solvents. Specifically, the present invention provides a recombinant protein prepared by obtaining various genes for various antibodies against female sex hormones, and modifying, by gene recombination technology, various properties of the original antibody, such as affinity, avidity, cross-reactivity, resistance for interfering substance on antigen-antibody reaction, resistance for interfering substance on enzymatic color developing reaction, resistance for solvent and the like.