PROBLEM TO BE SOLVED: To provide means that enables personal authentication implemented by acquiring data which causes low psychological resistance, is difficult to counterfeit, and well-reflects characteristics of a person with good reproducibility while eliminating or minimizing the necessity of maintenance work for preventing dirt on a device.SOLUTION: A personal authentication system uses a vein pattern of a finger. An amount of light irradiation of a light source is optimized based on a picked up finger image. An emphasizing process is performed on a vein pattern when performing image calculation for authentication.SELECTED DRAWING: Figure 5