Abstract: Disclosed is a gas chromatograph, which comprises a column oven which has a ventilation door disposed in an upper portion thereof and a hydrogen gas sensor installed in an upper region of an internal space thereof. Based on a detection signal from the hydrogen gas sensor, a control section determines a concentration of hydrogen gas contained in a gas within the column oven. If the concentration is equal to or greater than a given threshold value, the control section operates to open the ventilation door while cutting off current to be supplied to a heater, and closing a valve to stop supply of hydrogen gas. Thus, in the event of leakage of hydrogen gas, hydrogen gas accumulated within the column oven can be quickly released outside the column oven to avoid a risk of inflaming.