The present embodiment relates to a radiation detector having a structure enabling suppression of polarization in a thallium bromide crystalline body and suppression of corrosion of an electrode in the air. The radiation detector comprises a first electrode, a second electrode, and a thallium bromide crystalline body provided between the first and second electrodes. One of the first and the second electrodes includes an alloy layer and a low-resistance metal layer provide on the alloy layer. The alloy layer is comprised of an alloy of metallic thallium and another metal different from the metallic thallium. The low-resistance metal layer has a resistance value lower than a resistance value of the alloy layer and is electrically connected to a pad on a readout circuit while the radiation detector is mounted on the readout circuit.