PURPOSE: To enable beams to be taken out from a plural number of ion sources by using an outer electrode having a round concave surface and an inner electrode having a round convex surface to form a beam path in a deflector and making said electrodes freely rotatable.

CONSTITUTION: After ion sources 9a and 9b are connected to an electrostatic deflector 8, each beam is caused to strike a sample 7 placed in a measuring chamber after being passed through a transfer path 5 and a mass separator 4. The electrostatic deflector 8 is constituted of an outer electrode 10 having a round concave surface 11 and an inner electrode 12 having a round convex surface 14, which faces the concave surface 11 through a beam path 13. In addition, the electrodes 10 and 12 can be freely rotated by a rotation means 20 and a beam hole 13b is positioned facing the ion source 9a or 9b, so that analysis of the sample 7 is performed by causing two kinds of ions to strike the sample 7 alternately. As a result, it is possible to replace the ion source while maintaining the vacuum of an analyzer 1, thereby enabling its operation efficiency to be improved.