A detector unit for mammography of this invention includes a gamma-ray detector having a configuration with a cutout formed in part of a closed curve, a hollow portion thereof providing a field of view. The gamma-ray detector can easily be placed in a position where a breast and breast peripheries of a patient enter the field of view at the same time, by fitting sites of the patient not to be examined, such as a top of an arm and a shoulder, in the cutout. This allows breast tissues present in the breast and breast peripheries to be diagnosed at the same time.
