To provide an electron orbit calculation method capable of precisely calculating an electron orbit at high speed even in a system such that a space charge is present and the shape of the boundary is changed.

In this electron orbit computing equipment for calculating the orbit of an electron by determining the electric field of the space where the electron is moved when a space charge QB is present in a certain area Ω by use of boundary element method, approximation is performed by use of gauss distribution approximation method and point charge (δ function) approximation method according to the distance r between the present position S of the electron started from a point on the boundary Γ of the area and the space charge QB.