Apparatus for calculating current distribution inside brain includes: initial grid setting unit configured to set grid points constituting grid with predetermined pitch; current calculating unit configured to calculate current value at each grid point based on the electromagnetic information, by solving forward problem to obtain lead field matrix and by solving inverse problem to obtain current source vector; sub-grid setting unit configured to set grid points constituting sub-grid with smaller pitch, only for subset of the previously set grid, based on the current value at each grid point calculated in the preceding current calculating step; and calculation executing unit configured to repeat setting the sub-grid and calculating the current source vector by the sub-grid setting unit and the current calculating unit one or more times, after calculation of current source vector corresponding to the initial grid is executed by the initial grid setting unit and the current calculating unit.