In the gas chromatograph, a light source is provided in a column oven. Since a space in which the light source is disposed needs not to be secured outside the column oven, the size of the gas chromatograph can be reduced. A first connecting section in a sample introducing unit and a second connecting section in a detector are provided in an upper part in the column oven. The light source emits light toward the upper surface of the inside of the column oven (second inner casing). Therefore, light from the light source can be emitted toward the upper surface of the inside of the column oven where the first connecting section in the sample introducing unit and the second connecting section in the detector are provided and thus an operator frequently performs maintenance. Thus, work efficiency in the gas chromatograph can be improved.