A light receiving/emitting element module, comprising: a substrate; a light emitting element disposed on one principal face of the substrate; a light receiving element (3b, 3b1, 3b2) disposed on the one principal face of the substrate and disposed next to the light emitting element in a first direction; and an optical element (4, 4A, 4B1, 4B2, 4C, 4D1, 4D2) located away from the one principal face of the substrate, the optical element (4, 4A, 4B1, 4B2, 4C, 4D1, 4D2) comprising a first principal face (4s1) facing the one principal face, and a second principal face (4s2) opposed to the first principal face (4s1), the optical element (4, 4A, 4B1, 4B2, 4C, 4D1, 4D2) comprising a first lens (4a, 4a1) configured to direct light from the light emitting element, to a to-be-irradiated object, and a second lens (4b, 4b1, 4b2) configured to direct light reflected from the to-be-irradiated object, to the light receiving element (3b, 3b1, 3b2), the first lens (4a, 4a1) and the second lens (4b, 4b1, 4b2) being disposed side by side in the first direction, and a curved surface defining the first lens (4a, 4a1) and a curved surface defining the second lens (4b, 4b1, 4b2) which are disposed on at least one of the first principal face (4s1) and the second principal face (4s2), intersecting each other, wherein the first lens (4a, 4a1) and the second lens (4b, 4b1, 4b2) are configured so that a curved surface at the first principal face (4s1) of the first lens and a curved surface at the first principal face (4s1) of the second lens (4b, 4b1, 4b2) are joined to each other and a curved surface at the second principal face (4s2) of the first lens (4a, 4a1) and a curved surface at the second principal face (4s2) of the second lens (4b, 4b1, 4b2) are joined to each other, wherein, in each of the first lens and the second lens (4b, 4b1, 4b2), a radius of curvature of the curved surface at the first principal face (4s1) is smaller than a radius of curvature of the curved surface at the second principal face (4s2), or the first lens (4a, 4a1) and the second lens (4b, 4b1, 4b2) are defined by a single curved surface at the second principal face (4s2). a substrate; a light emitting element disposed on one principal face of the substrate; a light receiving element (3b, 3b1, 3b2) disposed on the one principal face of the substrate and disposed next to the light emitting element in a first direction; and an optical element (4, 4A, 4B1, 4B2, 4C, 4D1, 4D2) located away from the one principal face of the substrate, the optical element (4, 4A, 4B1, 4B2, 4C, 4D1, 4D2) comprising a first principal face (4s1) facing the one principal face, and a second principal face (4s2) opposed to the first principal face (4s1), the optical element (4, 4A, 4B1, 4B2, 4C, 4D1, 4D2) comprising a first lens (4a, 4a1) configured to direct light from the light emitting element, to a to-be-irradiated object, and a second lens (4b, 4b1, 4b2) configured to direct light reflected from the to-be-irradiated object, to the light receiving element (3b, 3b1, 3b2), the first lens (4a, 4a1) and the second lens (4b, 4b1, 4b2) being disposed side by side in the first direction, and a curved surface defining the first lens (4a, 4a1) and a curved surface defining the second lens (4b, 4b1, 4b2) which are disposed on at least one of the first principal face (4s1) and the second principal face (4s2), intersecting each other, wherein the first lens (4a, 4a1) and the second lens (4b, 4b1, 4b2) are configured so that a curved surface at the first principal face (4s1) of the first lens and a curved surface at the first principal face (4s1) of the second lens (4b, 4b1, 4b2) are joined to each other and a curved surface at the second principal face (4s2) of the first lens (4a, 4a1) and a curved surface at the second principal face (4s2) of the second lens (4b, 4b1, 4b2) are joined to each other, wherein, in each of the first lens and the second lens (4b, 4b1, 4b2), a radius of curvature of the curved surface at the first principal face (4s1) is smaller than a radius of curvature of the curved surface at the second principal face (4s2), or the first lens (4a, 4a1) and the second lens (4b, 4b1, 4b2) are defined by a single curved surface at the second principal face (4s2).