In a mask imaging method (by shooting a laser beam) for forming holes in a resin layer of a printed board, a sectional shape is reshaped by beam reshaping optics. Light path holes corresponding to the holes to be formed in the resin layer are used. The reshaped laser beam shoots the light path holes formed in the mask individually at once. Simultaneous passage of the laser beam through the light path holes formed in the mask is allowed, to form the holes in the resin layer. Exposure of the periphery and inside of a hole to the laser beam results in removal of a decomposition residue and/or processing residue.