PURPOSE: To reduce the number of parts installed on an ion engine for reduction of the weight of installation on a spacecraft by installing plural sets of electrostatic acceleration grids at a single ion source.

CONSTITUTION: In a discharging chamber 8, there are provided a pair of B accelerator grid 3 and B screen grid 4, and a pair of C accelerator grid 5 and C screen grid 6. There is also provided a combination of the same type of accelerator grid and screen grid in a perpendicular direction to the surface of a sheet. Moreover, there are also provided an electron generator 10 which generates electrons for main plasma generation, and a propellant feeder 9 which feeds propellant to the discharging chamber 8 and the electron generator 10. By installing an electrostatic acceleration grid consisting of plural sets of screen grids 2, 4, 6 and the accelerator grids 1, 3, 5, it is possible to generate thrust in an arbitrary direction.