Damping property of a damper utilizing a magnetic particle assemblage in the presence of magnetic field is investigated experimentally. The damping force depends on installation angle of the damper in the absence of magnetic field. In our study, one or two electromagnets are arranged near the edges of the damper case and we have found that effect of installation angle of the damper becomes small in the presence of magnetic field in this configuration. Applying magnetic field by two electromagnets arranged near the edge of the damper is useful method to suppress asymmetric damping property due to the gravitational force acting on the particles.