Abstract: An electromagnet comprises a pair of magnetic pole 1a and 1b, a return yoke 3, exciting coils 4 and 5, etc. In an interior portion of a magnetic pole, plural spacers 2a-2g are provided putting side by side in a horizontal direction. Each of the spaces 2a-2g is an air layer and a longitudinal cross-section is a substantially rectangular shape and the space has a lengthily extending slit shape in a vertical direction against a paper face in FIG. 1. The plural spaces are mainly arranged toward a right side from a beam orbit center O and an interval formed between adjacent spaces is narrower toward the right side. The electromagnet having a simple magnetic pole structure and a wide effective magnetic field area in a case where a maximum magnetic field strength is increased can be secured.