A medical image diagnosis apparatus of an embodiment includes a self-radioactive scintillator constituted of a single crystal; plural photon detectors that are arranged at various positions in the scintillator, and that output an electrical signal according to a quantity of radiation radiated from the scintillator; and calibration circuitry configured to calibrate an electrical signal output from each of the photon detectors such that calculation results based on the electrical signal output from each of the photon detectors are same among the photon detectors.