Abstract: Provided is a radiation detector 1 which is high in radiation detection sensitivity and is capable of preventing a loss of fluorescence by integrating scintillator crystals C and reflection plates rx and ry without using a permeable material. According to the present invention, the adhesive sheets Sa and Sb are adhered to the ends of scintillator crystals C arranged in a matrix in the height direction. The scintillator crystals C are integrated by the adhesive sheets Sa and Sb. According to the present invention, there is no need to form a scintillator 2 by securing the scintillator crystals C and the reflection plates ry by an adhesive. Therefore, an adhesive before curing does not enter gaps between the scintillator crystal C and the reflection plate ry, and therefore the gap forms an air layer.