A lens unit includes a first lens array including a plurality of first lens elements. The first lens array satisfies D1≤0.25·P1 where P1 is a pitch in a first direction between optical axes of adjacent ones of the first lens elements, and D1 is a displacement amount that is an absolute value of a difference between a first length WE1 from a center position of the first lens array to an end position of the first lens array in the first direction at a first temperature, and a second length WE2 from the center position of the first lens array to the end position of the first lens array at a second temperature higher than the first temperature by 30° C.