Lens and optical pick-up

An optical pick-up, comprising:

• a lens formed by injection molding;
• and
• a holder that accommodates the lens,
• wherein the lens comprises:
• a lens body having a first surface and a second surface;
• a flange part formed to protrude from a periphery of the lens body outward in a radial direction of the lens body, the flange part being formed to have a cylindrical outer circumferential surface centering on an optical axis of the lens;
• a lens installation surface formed at an outer edge part of the flange part on one of a side of the first surface and a side of the second surface;
• a recessed part formed as a part of the flange part such that a part of the cylindrical outer circumferential surface of the flange part is recessed toward the optical axis of the lens;
• and
• a gate root part which is a part of a gate of the lens, the gate root part being located at a central part of the recessed part,
• wherein:
• the gate root part has a flat surface which is in a same level with respect to the lens installation surface;
• and
• the gate root part lies on an optical axis side with respect to a virtual curved surface formed by extending the cylindrical outer circumferential surface of the flange part through the recessed part.