This paper investigated the characteristics of the magnetic field and the attractive magnetic force in a magnetic clutch of the automotive air conditioner. The magnetic force was calculated by using the finite element method, the principle of virtual work and the Maxwell stress tensor, and it was measured by experiment. Magnetic field is not affected by the pulley groove and the attractive magnetic force is also not significantly affected by the bearing because the total magnetic field in the airgap is not changed. The magnetic force increases rapidly as the airgap decreases. The bridges in the disk and the pulley decrease the magnetic force because they create the radial flux to saturation and reduce the effective axial magnetic flux in the airgap to the amount of the radial magnetic flux flowing in the bridges. Also the magnetic force is decreased proportionally as the increase of the cross-sectional area of bridge.