An electromagnetic field simulator for repeatedly calculating a space distribution of an electromagnetic field at a next point in time using a distribution of an electromagnetic field in a 3-dimensional space includes: a unit for calculating a distribution of an electric field and a distribution of an magnetic field on the entire 3-dimensional space; a unit for calculating a distribution of an electric field and a distribution of an magnetic field on a 2-dimensional space on a cut plane obtained by cutting the 3-dimensional space by a plane; a unit for setting an excitation condition of generating an electromagnetic wave by using a calculation result of the 2-dimensional electromagnetic field calculating unit; and a unit for generating an electromagnetic wave by forcibly vibrating a part of the electric field and the magnetic field in the 3-dimensional space on a basis of the excitation condition set.