PURPOSE: To enhance measuring sensitivity and to simplify measurement, by deactivating amylase contained in a specimen by an amylase inhibitor for specifically inhibiting amylase occurring from a higher animal to lower a blank value.

CONSTITUTION: The antigenic determinant possessing substance (ligand) contained in a specimen is contacted with a conjugate of an antibody to the ligand and amylase not substantially contained in the specimen in a solution. On the other hand, an amylase inhibitor for inhibiting the activity of amylase is brought into contact with amylase occurring from a higher animal contained in the specimen and a water insoluble high-molecular substance is contacted with this conjugant to perform enzymatic reaction and the activity of amylase is measured. By this method, the ligand in a specimen containing amylase such as human serum can be measured with high sensitivity and operation is also simple and inexpensive quantitative analysis of the ligand is enabled.