A light guide, comprising: a rod-like main body (551 H) which is capable of guiding light in a longitudinal direction; an input surface which is provided on one end of the main body and on which the light is inputted; a rear end surface (551 c) which is provided on another end of the main body and opposite to the input surface; an output surface which is provided on the main body, from which the light is emitted in a direction intersecting with the longitudinal direction and which is long in the longitudinal direction; a reflecting surface (551 b) which is a surface provided on the main body and opposite to the output surface; a first diffusing portion which is formed on a part of the reflecting surface from the input surface to a preset reference position and diffuses light; and a second diffusing portion which is formed on a part of the reflecting surface from the reference position to the rear end surface (551 c) and diffuses light; wherein: the preset reference position is set at a position in the longitudinal direction in which the illuminance of reflected light which is reflected twice or more in the light guide exceeds the illuminance of reflected light which is reflected once or less in the light guide as a distance from the input surface increases when a diffusing portion, which is formed on the reflecting surface and diffuses light, has a constant length in a direction orthogonal to the longitudinal direction along the longitudinal direction; the first diffusing portion has a first length in the direction orthogonal to the longitudinal direction; the second diffusing portion has a second length in the direction orthogonal to the longitudinal direction; and the first length is longer than the second length, wherein the first diffusing portion includes a plurality of recesses which are formed at intervals along the longitudinal direction, extend in a direction perpendicular to the longitudinal direction and function as prisms; the second diffusing portion includes a plurality of recesses which are formed at intervals along the longitudinal direction, extend in the direction perpendicular to the longitudinal direction and have a shorter length in the direction perpendicular to the longitudinal direction than the recesses in the first diffusing portion and function as prisms, wherein each of the plurality of recesses has a first prism surface formed on the input surface side and a second prism surface formed on a side opposite to the input surface; wherein an angle formed by the second prism surface of each recess included in the second diffusing portion and the longitudinal direction on the side opposite to the input surface is in the range of 90° to 95°, wherein an angle formed by the second prism surface of each recess included in the first diffusing portion and the longitudinal direction on the side opposite to the input surface is in the range of 130° to 140°, wherein an angle formed by the first prism surface of each recess included in the first diffusing portion and the longitudinal direction on the input surface side is in the range of 90° to 95°, and wherein an angle formed by the first prism surface of each recess included in the second diffusing portion and the longitudinal direction on the input surface side is in the range of 130° to 140°. a rod-like main body (551 H) which is capable of guiding light in a longitudinal direction; an input surface which is provided on one end of the main body and on which the light is inputted; a rear end surface (551 c) which is provided on another end of the main body and opposite to the input surface; an output surface which is provided on the main body, from which the light is emitted in a direction intersecting with the longitudinal direction and which is long in the longitudinal direction; a reflecting surface (551 b) which is a surface provided on the main body and opposite to the output surface; a first diffusing portion which is formed on a part of the reflecting surface from the input surface to a preset reference position and diffuses light; and a second diffusing portion which is formed on a part of the reflecting surface from the reference position to the rear end surface (551 c) and diffuses light; the preset reference position is set at a position in the longitudinal direction in which the illuminance of reflected light which is reflected twice or more in the light guide exceeds the illuminance of reflected light which is reflected once or less in the light guide as a distance from the input surface increases when a diffusing portion, which is formed on the reflecting surface and diffuses light, has a constant length in a direction orthogonal to the longitudinal direction along the longitudinal direction; the first diffusing portion has a first length in the direction orthogonal to the longitudinal direction; the second diffusing portion has a second length in the direction orthogonal to the longitudinal direction; and the first length is longer than the second length,