A remarkable conversion efficiency from laser to protons is demonstrated by particle simulations in a laser-foil interaction. The total laser-proton conversion efficiency becomes 16.7% in an optimized multi-hole target, though a conventional plane foil target serves a low efficiency. When an intense short-pulse laser illuminates the thin foil target, the foil electrons are accelerated around the target by the intense laser. The hot electrons generate a strong electric field, which accelerates the foil protons, and the proton beam is generated. In our previous study, we found that multihole thin-foil target was efficient for the energy conversion from laser to protons [Phys. Rev. E 78, 046401 (2008)], and the energy conversion efficiency was 9.3%. In this paper the results clarify the role of the target hole thickness and depth in the laser-proton energy conversion. The optimized multi-hole foil target provides a remarkable increase in the laser-proton energy conversion efficiency.