A method for conveniently detecting binding between the von Willebrand factor and glycoprotein Ib and a means to be used therein. The von Willebrand factor fixed in a reactor immobilized in a reaction vessel in the presence of bottrocetin is bound to a chimeric protein constructed by fusing the carboxyl terminal of a partial protein containing the von Willebrand factor-binding site of glycoprotein Ib with the amino terminal of the Fc region of an immunoglobulin molecule. Then the Fc region of the above immunoglobulin molecule is detected to thereby detect the binding between the von Willebrand factor and the glycoprotein Ib or inhibition of this binding.