We have developed a new galactic chemodynamical evolution code, called GCD+, for studies of galaxy formation and evolution. This code is based on our original three-dimensional tree N-body/smoothed particle hydrodynamics code which includes self-gravity, hydrodynamics, radiative cooling, star formation, supernova feedback and metal enrichment. GCD+ includes a new Type II (SNe II) and Ia (SNe Ia) supernovae model, taking into account the lifetime of progenitor stars and chemical enrichment from intermediate-mass stars. We apply GCD+ to simulations of elliptical galaxy formation, and examine the colour-magnitude relation (CMR), the Kormendy relation, and the [Mg/Fe]-magnitude relation of simulation end-products. GCD+ is a useful and unique tool which enables us to compare simulation results with the observational data directly and quantitatively. Our simulation confirm the results of Kawata, who uses a simpler chemodynamical evolution code. We newly find that radiative cooling becomes more efficient and thus the gas infall rate increases, with decreasing mass of galaxies, which contributes to the slope of the CMR. In addition, the sophisticated treatments of both SNe II and SNe Ia in GCD+ show that feedback from SNe Ia plays a crucial role in the evolution of elliptical galaxies. We conclude that the feedback effect of SNe Ia should not be ignored in studying the evolution of elliptical galaxies.