A radiation detector comprising: a scintillator panel (10, 10A) emitting scintillation light in response to incident radiation; and a photo-detection substrate facing the scintillator panel and detecting the scintillation light, wherein the scintillator panel comprises: a substrate portion (11, 11A) having a first main surface and a first rear surface intersecting a first direction on sides opposite to each other, and a first side surface extending such that the first main surface and the first rear surface are joined to each other; and a scintillator layer portion having a second rear surface formed of a plurality of columnar crystals extending in the first direction and formed to include a base portion being on one end side of the columnar crystals and facing the first main surface, a second main surface formed to include a tip portion on the other end side of the columnar crystals, and a second side surface extending such that the second main surface and the second rear surface are joined to each other, wherein the first side surface and the second side surface are substantially flush with each other, wherein the scintillator panel (10, 10A) has a panel main surface, wherein the photo-detection substrate has a main surface, wherein the panel main surface faces the main surface of the photo-detection substrate, and wherein the scintillator panel (10, 10A) is adhered to the main surface of the photo-detection substrate, characterized in that, in the substrate portion (11, 11 A), an angle between the first rear surface and the first side surface is smaller than 90 degrees. a scintillator panel (10, 10A) emitting scintillation light in response to incident radiation; and a photo-detection substrate facing the scintillator panel and detecting the scintillation light, wherein the scintillator panel comprises: a substrate portion (11, 11A) having a first main surface and a first rear surface intersecting a first direction on sides opposite to each other, and a first side surface extending such that the first main surface and the first rear surface are joined to each other; and a scintillator layer portion having a second rear surface formed of a plurality of columnar crystals extending in the first direction and formed to include a base portion being on one end side of the columnar crystals and facing the first main surface, a second main surface formed to include a tip portion on the other end side of the columnar crystals, and a second side surface extending such that the second main surface and the second rear surface are joined to each other, a substrate portion (11, 11A) having a first main surface and a first rear surface intersecting a first direction on sides opposite to each other, and a first side surface extending such that the first main surface and the first rear surface are joined to each other; and a scintillator layer portion having a second rear surface formed of a plurality of columnar crystals extending in the first direction and formed to include a base portion being on one end side of the columnar crystals and facing the first main surface, a second main surface formed to include a tip portion on the other end side of the columnar crystals, and a second side surface extending such that the second main surface and the second rear surface are joined to each other, wherein the first side surface and the second side surface are substantially flush with each other, wherein the scintillator panel (10, 10A) has a panel main surface, wherein the photo-detection substrate has a main surface, wherein the panel main surface faces the main surface of the photo-detection substrate, and wherein the scintillator panel (10, 10A) is adhered to the main surface of the photo-detection substrate, characterized in that, in the substrate portion (11, 11 A), an angle between the first rear surface and the first side surface is smaller than 90 degrees.