A remarkable improvement is presented on the energy conversion efficiency from laser to protons in a laser-foil interaction by particle simulations. The total laser-proton energy conversion efficiency from laser to protons becomes 16.7%, though a conventional plane foil target serves a rather low efficiency. In our 2.5-dimensional particle-in-cell simulations the Al multihole structure is also employed, and the laser absorption ratio reaches 71.2%. The main physical reason for the enhancement of the conversion efficiency is a reduction of the laser reflection at the target surface area;