1. An area exposure dosimetry method comprising: calculating an area of an irradiation region, and at least one of an area of an object region and an area of a non-object region in a radiation image obtained by radiographing an object; acquiring an effective dose of radiation from a radiation generator; and calculating an area exposure dose as a radiation dose of the object on the basis of the area of the irradiation region, the calculated one of the area of the object region and the area of the non-object region, and the effective dose.