1. A method for reconstructing a local high resolution X-ray CT image, comprising: acquiring projection data by means of irradiation of X-rays on a target object at a position close to an X-ray generator such that a portion of the target object including a local region of interest exists within a range of irradiation angles of X-rays; calculating virtual projection data on the assumption that the X-rays are irradiated on the entire target object at the close position, based on projection data acquired through irradiation of the X-rays on the entire target object at a position where the entire target object exists within the range of irradiation angles of X-rays; combining the virtual projection data on the entire target object except data on the local region of interest with the projection data acquired at the position close to the X-ray generator; and reconstructing the combined projection data.