The Standard Model achieved significant success with the discovery of the Higgs in 2012. However, there are still numerous unexplained phenomena. One of them is the number of generations problem, where quarks and leptons come in three copies with only differences in mass while having identical spin and charge. Is the existence of these three generations a mere coincidence, or is there a deeper reason behind it? The Standard Model cannot explain why there are three generations.On the other hand, the higher dimensional theory offers a possible explanation for the number of generations problem. In the higher dimensional theory, the number of generations is related to the geometry of the extra dimensions. In other words, the number of generations carries a physical meaning associated with the geometry of the extra dimensions. In this seminar, I will talk about the generation structure of the T^2/Z_N orbifold with magnetic flux.