A gas analyzing apparatus comprising: a tube-like member (11; 115, 132) that includes a light path through which measurement light is emitted to a predetermined measurement region of sample gas flowing in a pipe (50; 150) and/or through which the measurement light from the measurement region is received; an optical system member (12, 20; 111, 131) configured to emit the measurement light to the sample gas in the measurement region and/or to receive the measurement light from the measurement region; a purge gas feed tube (26; 120, 136) having a hollow portion including: a purge gas flow path through which the purge gas (Pa) is supplied to the region between the optical system member (12, 20; 111, 131) and the measurement region; and the light path for the measurement light, the purge gas feed tube being provided inside of the tube-like member defining a first gap (28; 144, 135) between it and an inner wall of the tube-like member (11; 115, 132); a first purge gas feed portion (22; 121, 137) for feeding purge gas into the purge gas feed tube; a second purge gas feed portion (23; 123, 139) for feeding purge gas into the first gap (28; 144, 125); and a flange (13; 116, 133) configured to be attached to an attachment portion (52; 152, 160) of an opening (53; 153, 161) of the pipe side wall (51; 151), wherein a second gap (56; 155, 163) is defined between an outer circumferential surface of the tube-like member (11; 115, 132) and an inner circumferential surface of the attachment portion, the second gap communicating with the pipe; characterized in that the purge gas feed tube (26; 120, 136) has a smooth inner diameter so as not to generate a turbulent flow, the purge gas (Pa) flowing through the hollow portion of the purge gas feed tube (26; 120, 136) is a laminar flow, a distal end (27; 129) of the purge gas feed tube (26; 120, 136) is disposed close to an end portion of the measurement region, and the first purge gas feed portion (22; 121, 137) and the second purge gas feed portion (23; 123, 139) are separate members. a tube-like member (11; 115, 132) that includes a light path through which measurement light is emitted to a predetermined measurement region of sample gas flowing in a pipe (50; 150) and/or through which the measurement light from the measurement region is received; an optical system member (12, 20; 111, 131) configured to emit the measurement light to the sample gas in the measurement region and/or to receive the measurement light from the measurement region; a purge gas feed tube (26; 120, 136) having a hollow portion including: a purge gas flow path through which the purge gas (Pa) is supplied to the region between the optical system member (12, 20; 111, 131) and the measurement region; and the light path for the measurement light, the purge gas feed tube being provided inside of the tube-like member defining a first gap (28; 144, 135) between it and an inner wall of the tube-like member (11; 115, 132); a first purge gas feed portion (22; 121, 137) for feeding purge gas into the purge gas feed tube; a second purge gas feed portion (23; 123, 139) for feeding purge gas into the first gap (28; 144, 125); and a flange (13; 116, 133) configured to be attached to an attachment portion (52; 152, 160) of an opening (53; 153, 161) of the pipe side wall (51; 151), wherein a second gap (56; 155, 163) is defined between an outer circumferential surface of the tube-like member (11; 115, 132) and an inner circumferential surface of the attachment portion, the second gap communicating with the pipe; characterized in that the purge gas feed tube (26; 120, 136) has a smooth inner diameter so as not to generate a turbulent flow, the purge gas (Pa) flowing through the hollow portion of the purge gas feed tube (26; 120, 136) is a laminar flow, a distal end (27; 129) of the purge gas feed tube (26; 120, 136) is disposed close to an end portion of the measurement region, and the first purge gas feed portion (22; 121, 137) and the second purge gas feed portion (23; 123, 139) are separate members.