A light source module comprising: a light source having an upper surface comprising a light emission surface; and a light guide member comprising a lens portion having a central axis that extends through a center of the light emission surface, wherein the lens portion comprises: an incidence surface that is recessed and opposes the light emission surface of the light source such that light from the light source is incident on the incidence surface, a reflection surface disposed outward of the incidence surface and configured to reflect part of the light that is incident on the incidence surface to an outside, and an emitting surface configured to emit part of the light that is incident on the incidence surface and the light reflected at the reflection surface, wherein the incidence surface comprises an upper incidence region positioned on an upper side, and a lower incidence region positioned lower than the upper incidence region, in a cross section that includes the central axis, wherein the lower incidence region has 2-fold rotational symmetry relative to the central axis, wherein the lower incidence region comprises a first lower incidence region, and a second lower incidence region at a position rotated by 45 degrees from the first lower incidence region, and wherein a height of the second lower incidence region is greater than a height of the first lower incidence region, characterised in that an angle formed between the lower incidence region and a horizontal plane is greater than an angle formed between the upper incidence region and the horizontal plane. a light source having an upper surface comprising a light emission surface; and a light guide member comprising a lens portion having a central axis that extends through a center of the light emission surface, wherein the lens portion comprises: an incidence surface that is recessed and opposes the light emission surface of the light source such that light from the light source is incident on the incidence surface, a reflection surface disposed outward of the incidence surface and configured to reflect part of the light that is incident on the incidence surface to an outside, and an emitting surface configured to emit part of the light that is incident on the incidence surface and the light reflected at the reflection surface, an incidence surface that is recessed and opposes the light emission surface of the light source such that light from the light source is incident on the incidence surface, a reflection surface disposed outward of the incidence surface and configured to reflect part of the light that is incident on the incidence surface to an outside, and an emitting surface configured to emit part of the light that is incident on the incidence surface and the light reflected at the reflection surface, wherein the incidence surface comprises an upper incidence region positioned on an upper side, and a lower incidence region positioned lower than the upper incidence region, in a cross section that includes the central axis, wherein the lower incidence region has 2-fold rotational symmetry relative to the central axis, wherein the lower incidence region comprises a first lower incidence region, and a second lower incidence region at a position rotated by 45 degrees from the first lower incidence region, and wherein a height of the second lower incidence region is greater than a height of the first lower incidence region, characterised in that an angle formed between the lower incidence region and a horizontal plane is greater than an angle formed between the upper incidence region and the horizontal plane.