An exposure unit for an image forming apparatus, comprising: a light-emitting element array including a plurality of light-emitting elements that are disposed in a first direction and each emit a light beam; and a lens array that faces the light-emitting element array in a second direction that is orthogonal to the first direction, and focuses the light beams emitted from the respective light-emitting elements, the second direction being an optical axis direction, characterized in that the following expression is satisfied, and a symmetric property, determined from the following expression, of a light amount distribution (E) in the first direction of at least one of the light beams focused by the lens array satisfies the following expressions and, S = HL − HR / XE / 2 0 ≤ S ≤ 0.65 Lo ≠ LB S / So ≤ 1.3 where S is the symmetric property of the light amount distribution (E) in the first direction of any of the light beams focused by the lens array, XE is a dimension of any of the light-emitting elements in the first direction, HL is a difference between a local maximum position and a first local minimum position that are adjacent to each other in the light amount distribution (E) in the first direction of any of the light beams focused by the lens array, HR is a difference between the local maximum position and a second local minimum position in the light amount distribution (E) in the first direction of any of the light beams focused by the lens array, the second local minimum position being adjacent to the local maximum position and located on an opposite side of the local maximum position to the first local minimum position, Lo is a distance from the light-emitting element array to an end surface of the lens array, and LB is a back focal distance of the lens array in which a contrast becomes maximum, the contrast being determined from the light amount distribution (E) in the first direction of any of the light beams focused by the lens array, and where So is a local minimum value of the symmetric property S, the symmetric property depending on a change in a value of | Lo - LB |. a light-emitting element array including a plurality of light-emitting elements that are disposed in a first direction and each emit a light beam; and a lens array that faces the light-emitting element array in a second direction that is orthogonal to the first direction, and focuses the light beams emitted from the respective light-emitting elements, the second direction being an optical axis direction, characterized in that the following expression is satisfied, and a symmetric property, determined from the following expression, of a light amount distribution (E) in the first direction of at least one of the light beams focused by the lens array satisfies the following expressions and, S = HL − HR / XE / 2 0 ≤ S ≤ 0.65 Lo ≠ LB S / So ≤ 1.3 where S is the symmetric property of the light amount distribution (E) in the first direction of any of the light beams focused by the lens array, XE is a dimension of any of the light-emitting elements in the first direction, HL is a difference between a local maximum position and a first local minimum position that are adjacent to each other in the light amount distribution (E) in the first direction of any of the light beams focused by the lens array, HR is a difference between the local maximum position and a second local minimum position in the light amount distribution (E) in the first direction of any of the light beams focused by the lens array, the second local minimum position being adjacent to the local maximum position and located on an opposite side of the local maximum position to the first local minimum position, Lo is a distance from the light-emitting element array to an end surface of the lens array, and LB is a back focal distance of the lens array in which a contrast becomes maximum, the contrast being determined from the light amount distribution (E) in the first direction of any of the light beams focused by the lens array, and where So is a local minimum value of the symmetric property S, the symmetric property depending on a change in a value of | Lo - LB |.