A lens holding structure, comprising: a first holding member; a first lens disposed ahead of the first holding member; a second lens disposed ahead of the first lens; a second holding member disposed ahead of the second lens; and a fixing unit that fixes the first holding member and the second holding member in a state of holding the first lens and the second lens between the first holding member and the second holding member, wherein the first lens and the second lens are held between the first holding member and the second holding member in a state of an optical surface of the second lens being surface-contacted with an optical surface of the first lens, and wherein a first space is formed between a portion of the first lens other than the optical surface of the first lens and the second lens, the lens holding structure further comprising: a heat sink disposed behind the first holding member; a light source module fixed on the front surface of the heat sink; and a third lens disposed ahead of the second lens, wherein the first holding member includes a first portion which comes into contact with the front surface of the heat sink; wherein the second lens includes a flange unit; wherein the second holding member includes a second portion which comes into contact with the front surface of the heat sink, and a presser unit which presses down on the flange unit of the second lens; wherein the third lens includes a third portion which comes into contact with the second portion of the second holding member; and wherein the fixing unit fixes the first holding member and the second holding member in a state of the first portion of the first holding member abutting the front surface of the heat sink, the second portion of the second holding member abutting the front surface of the heat sink, the third portion of the third lens abutting the second portion of the second holding member, and the presser unit of the second holding member abutting the flange unit of the second lens. a first holding member; a first lens disposed ahead of the first holding member; a second lens disposed ahead of the first lens; a second holding member disposed ahead of the second lens; and a fixing unit that fixes the first holding member and the second holding member in a state of holding the first lens and the second lens between the first holding member and the second holding member, wherein the first lens and the second lens are held between the first holding member and the second holding member in a state of an optical surface of the second lens being surface-contacted with an optical surface of the first lens, and wherein a first space is formed between a portion of the first lens other than the optical surface of the first lens and the second lens, the lens holding structure further comprising: a heat sink disposed behind the first holding member; a light source module fixed on the front surface of the heat sink; and a third lens disposed ahead of the second lens, wherein the first holding member includes a first portion which comes into contact with the front surface of the heat sink; wherein the second lens includes a flange unit; wherein the second holding member includes a second portion which comes into contact with the front surface of the heat sink, and a presser unit which presses down on the flange unit of the second lens; wherein the third lens includes a third portion which comes into contact with the second portion of the second holding member; and wherein the fixing unit fixes the first holding member and the second holding member in a state of the first portion of the first holding member abutting the front surface of the heat sink, the second portion of the second holding member abutting the front surface of the heat sink, the third portion of the third lens abutting the second portion of the second holding member, and the presser unit of the second holding member abutting the flange unit of the second lens. a heat sink disposed behind the first holding member; a light source module fixed on the front surface of the heat sink; and a third lens disposed ahead of the second lens, wherein the first holding member includes a first portion which comes into contact with the front surface of the heat sink; wherein the second lens includes a flange unit; wherein the second holding member includes a second portion which comes into contact with the front surface of the heat sink, and a presser unit which presses down on the flange unit of the second lens; wherein the third lens includes a third portion which comes into contact with the second portion of the second holding member; and wherein the fixing unit fixes the first holding member and the second holding member in a state of the first portion of the first holding member abutting the front surface of the heat sink, the second portion of the second holding member abutting the front surface of the heat sink, the third portion of the third lens abutting the second portion of the second holding member, and the presser unit of the second holding member abutting the flange unit of the second lens.