The breast cancer detector of the invention comprising a transparent breast pressing member 1 having a pressing face 4 which is pressed to a breast of a subject that makes it possible to observe the breast pressed to the body from the opposite face to the pressing face 4, a light source means 2 for irradiating light of a designated wavelength with respect to the breast in an area to which the pressing face 4 is pressed and an image pickup means 3 sensitive to light from the breast derived from irradiated light of the light source means 2 and obtaining the breast image through the breast pressing member 1, wherein breast cancer is detected from the breast image obtained by the image pickup means. Therefore, the breast is pressed to the body by using the breast pressing member 1 to keep the breast thin, thus making it possible to irradiate uniformly the light emitted from the light source 2 to an area of the breast to which the pressing face 4 is pressed. The light from the breast derived from the irradiated light is obtained from the image pickup means 3 to detect breast cancer in the breast from the thus-obtained image.