Recently, magnetic bearings with non-contact levitation have been researched to overcome the deficiencies of the mechanical ball bearings. An active magnetic bearing (AMB) works on the principle of electromagnetic levitation and consists of many electromagnets, power amplifiers, controllers, and gap sensors with associated electronics to provide the feedback required to control the position of the rotor within the gap. This paper deals with a four-pole active magnetic bearing. Firstly, basic structure and mathematical model of the active magnetic bearing are described and discussed in detail. The principle of a feedback control strategy for the active magnetic bearing is then introduced. Based on the analysis of the mathematical model of the active magnetic bearing, the design of a proportiona/integral-derivative (PID) controller is explained in order to realize stable magnetic levitation. Finally, an experimental setup of the four-pole active magnetic bearing is developed in order to confirm the proposed control method. The experimental results show that the magnetic bearing can work stably in all radial directions and the rigid body is levitated without any contact.