A gas processing device includes: a casing that includes a first end having a first opening region constituting an intake port, a second end having a second opening region constituting an exhaust port, and a main body portion on the inside of which is formed a hollow portion; a discharge lamp that has a tube body which is disposed in the hollow portion and which has a shape extending in the first direction, a first electrode, and a second electrode, the discharge lamp that emits ultraviolet rays from the tube body; a power supply unit arranged outside the casing; and a first power supply line and a second power supply line that are wired so as to pass through a side closer to the first end than the main body portion, and that electrically connect the power supply unit to the first electrode and the second electrode.