A lens array can have monitor light reliably and can be manufactured easily. With this lens array (2), a reflecting/transmission surface (15) of a first concave part (14) branches laser lights L having been emitted from light emitting elements (7) and having been incident on first lens surfaces (11), toward second lens surfaces (12) and third lens surfaces (13). Monitor lights M branched toward the third lens surfaces (13) are emitted from the third lens surfaces (13) toward first light receiving elements (8) passing through a refracting surface (19) of a second concave part (18). The lens array (2) is formed such that the optical axes on the first lens surfaces (11) and the optical axes on the third lens surfaces (13) are parallel, and the optical axes on the first lens surface (11) and the optical axes on the second lens surfaces (12) are parallel or vertical.