In the attenuation coefficient image estimation method of the present invention, an attenuation coefficient value is corrected in Step S8 (μ=μ′；+α×μoff) based on a mathematical relationship in which the difference between a value of a non-quantitative image μ′； in a region Ω and a known attenuation coefficient value (a value of a true attenuation coefficient image) can be approximated by α×μoff obtained by multiplying an offset image μoff by a coefficient α. Therefore, in the attenuation coefficient image having the attenuation coefficient value μ corrected in Step S8 (μ=η′；+α×μoff), a systematic error becomes small. As a result, a quantitative attenuation coefficient image can be generated, which enables accurate attenuation correction of the radioactivity image.
