A light guide plate display device adapted to display a plurality of patterns (A, B, C, D), the light guide plate display device comprising: a light guide plate which includes a display face and a rear face on a side opposite to the display face and a plurality of end faces, and is formed of a light transmitting material; a plurality of light source devices which are provided along the plurality of end faces of the light guide plate, respectively, and radiate light from the respective plurality of end faces of the light guide plate toward an inside of the light guide plate, and a plurality of prisms which are formed inside the light guide plate, wherein the respective plurality of prisms have a plurality of side faces which face the respective plurality of light source devices, wherein the side faces facing one of the light source devices are inclined in at least two stages of a transmitting inclined face (β) which transmits light radiated from the light source device, and a reflecting inclined face (α) which reflects the light radiated from the respective plurality of light source devices, and outputs the light to the display face, in a thickness direction which is perpendicular to the display face of the light guide plate, and wherein an angle (Θ α) formed by the reflecting inclined face (α) and a line parallel to the rear face is smaller than an angle (Θ β) formed by the transmitting inclined face (β) and the rear face; characterized in that in prisms of the plurality of prisms which are located at a portion of one of the plurality of different patterns (A, B, C, D), an area of the reflecting inclined face (α) on a side face which faces the respective light source device is set to be large to improve luminance and in a prism which is not located at a portion of the one of the plurality of different patterns (A, B, C, D), an area of the reflecting inclined face (α) on the side face which faces the respective light source device is set to be small to decrease luminance. a light guide plate which includes a display face and a rear face on a side opposite to the display face and a plurality of end faces, and is formed of a light transmitting material; a plurality of light source devices which are provided along the plurality of end faces of the light guide plate, respectively, and radiate light from the respective plurality of end faces of the light guide plate toward an inside of the light guide plate, and a plurality of prisms which are formed inside the light guide plate, wherein the respective plurality of prisms have a plurality of side faces which face the respective plurality of light source devices, wherein the side faces facing one of the light source devices are inclined in at least two stages of a transmitting inclined face (β) which transmits light radiated from the light source device, and a reflecting inclined face (α) which reflects the light radiated from the respective plurality of light source devices, and outputs the light to the display face, in a thickness direction which is perpendicular to the display face of the light guide plate, and wherein an angle (Θ α) formed by the reflecting inclined face (α) and a line parallel to the rear face is smaller than an angle (Θ β) formed by the transmitting inclined face (β) and the rear face; characterized in that in prisms of the plurality of prisms which are located at a portion of one of the plurality of different patterns (A, B, C, D), an area of the reflecting inclined face (α) on a side face which faces the respective light source device is set to be large to improve luminance and in a prism which is not located at a portion of the one of the plurality of different patterns (A, B, C, D), an area of the reflecting inclined face (α) on the side face which faces the respective light source device is set to be small to decrease luminance.