Shaking table tests were conducted on foundation models to elucidate the dynamic behavior of existing foundations strengthened with micropiles and verify the effect of such seismic retrofit. The tests were then simulated by numerical analysis. Three models were used in the tests: a model representing the existing piles, model strengthened with vertical micropiles added in the front and back of the existing foundations, and model strengthened with battered micropiles. As the results of simulation by nonlinear seismic response analysis agreed well with the results of the experiments, the strengthening effect of micropiles was confirmed both by testing and numerical simulation.