The present invention provides a lens (i.e., luminous flux control member) for an optical element of a backlight, capable of easily aligning the orientation in the plane direction. The luminous flux control member according to the present invention includes a lens main body and legs. The lens main body includes a light-entering area for light emitted from a light-emitting element to enter on the lower surface side and a light-emitting area for emitting the light entered from the light-entering area to the outside on the upper surface side. The legs are legs for mounting the luminous flux control member on a substrate on which the light-emitting element is mounted and are disposed on the lower surface of the lens main body so as to project downward. The luminous flux control member satisfies the following condition 1 or 2: (Condition 1) at least one of the legs is accommodated in one of two grooves having different widths, and all of the other legs are accommodated in the other groove only when the lens main body is oriented in one predetermined direction or an opposite direction thereto; and (Condition 2) the lens main body or all of the legs are accommodated in one groove only when the lens main body is oriented in one predetermined direction or an opposite direction thereto.