PURPOSE: To provide a sulfur concentration measuring apparatus capable measuring even pertroleum oil (e.g., kerosene) with a lower content of sulfur.

CONSTITUTION: This apparatus is provided with a radiation source 20 which radiates radiation energy equal in radiation absorption coefficient of hydrogen and carbon, a solution to be measured comprising hydrogen, carbon and sulfur passing through a radiation radiated from the radiation source 20, a control liquid comprising hydrogen and carbon. containing no sulfur, passing through the radiation radiated from the radiation source 20 and a radiation detector 12 which detects the intensity of the radiation passing through the liquid to be measured and the control liquid separately as ionization current. Moreover, an arithmetic means 13 which divides an ionization current value on the liquid to be measured as detected by that on the side of the control liquid while performing a logarithmic conversion of the quotients to obtain a signal proportional to the concentration of sulfur of the liquid to be measured.