A method for detecting blood component in a sample comprising reacting a human erythrocyte membrane band 3 glycoprotein (band 3) in the sample and a hemagglutinin produced by a microorganism belonging to the genus Conidiobolus (CA) and measuring said band 3 glycoprotein contained in a complex produced by the reaction. Because band 3 can be detected specifically, at high sensitivity, and stably by the use of CA, the method ensures qualitative or quantitative, and accurate detection of human blood component in feces or contents of digestive organs, of which the determination of the presence or quantity of human blood component by hemoglobin is difficult.