PURPOSE: To obtain a focus state near a true circle with a simple structure by providing two four-electrode lenses.

CONSTITUTION: An electron gun 1 is provided with unipotential type four- electrode lenses 13, 14 and a scan expanding lens 4 as a bipotential type four- electrode lens. The lens 13 acts as a convex lens in the vertical direction and as a concave lens in the horizontal direction, the lens acts as a thick convex lens in the vertical direction and as a thin concave lens in the horizontal direction respectively, the horizontal deflection beam is deflected and expanded in the lens 4, and the vertical deflection beam is reversed in its advance direction and deflected and expanded. The distance between an object point 49 and the lens 13 and the distance between the lenses 13, 14 are made nearly equal, and a focus state near a true circle is obtained on a screen 6.