By using the electromagnetic excitation modes in ferromagnetic superconductors, which are the coupled modes of the photon, electric current and magnetic moments, the reflection and transmission coefficients, Rf and Tf, are calculated for the electromagnetic wave incident normally on the surface of a film of ferromagnetic superconductor. It is shown that Rf and Tf oscillate as a function of the film thickness, reflecting the oscillatory character of the excitation modes, and that Rf and Tf have an anomally at the magnetic phase transition temperature Ts. © 1985.