Graphical explanation of transition process is given on two kinds of improper ferroelectrics, one kind contains crystals where order parameter and polarization have the same symmetry, the other one where they have different symmetries. Peculiar dielectric, electromechanical and optical properties of improper ferroelectrics are discussed by taking Ca2Sr(C2H5CO2)6 as the most definitive example. The importance of anomalous enhancement of the electrogyration effect of optically active improper ferroelectrics is stressed.