We observe the proton signals produced by laser interaction with thin-foil targets of polyimide and of copper. We change the thickness of the polyimide target to 7.5 μm, 12.5 μm, and 50 μm. High-energy protons with the maximum energy of ~2.3 MeV from 7.5 μm thick polyimide are observed. This proton beam with the maximum energy of multi-MeV has various applications such as a proton shadowgraphy.