On magnetic particles serving as a first support, an antibody against a nonspecific reaction factor is immobilized. These magnetic particles are mixed with a specimen and suspended therein. After suspending, the suspension is sucked up into a pipette chip and a magnet comes close to the pipette chip. While remotely constraining with the magnet the magnetic particles carrying the nonspecific reaction factor bonded thereto, the residual liquid is discharged into a well. Thus, the removal of a contaminant contained in the specimen is completed. The thus treated specimen discharged into the well is subjected to an immunoassay. The magnetic particles carrying the antibody immobilized thereon are mixed with the treated specimen and suspended therein. The suspension is sucked up into a pipette chip and the magnetic particles carrying an antigen bonded thereto are separated by use of the magnet. The magnetic particles carrying the antigen bonded thereto are washed, mixed with an enzyme-labeling solution, which contains a second support, and suspended therein. After suspending, the magnetic particles being labeled and carrying the antigen bonded thereto are mixed with a substrate solution and subjected to the measurement of emission intensity, etc.