PURPOSE: In a photoelectric converting tube for detecting NOX in the air due to the exhaust gas from a car, to detect the light emission from the fluid efficiently by forming a photoconductive face along the axis of the through-holes arranged between the bottom face and the top while sorrounding the axis.
CONSTITUTION: A vacuum air-tight container 1 is choked by a tube 11, bottom face 12 and a hemisphere 13 while through-holes 15 are formed by the tube 14 coaxial with said tube 11 between the center of the bottom face 12 and the top of the hemisphere 13. A photoelectric face 2 is formed on the inner face of the hemisphere 13 and the outer wall of the tube 14 or a portion of the inner wall of the container 1. Dinodes 31W34 and 4 are provided in the container 1 to multiply the incident primary electron and to emit the secondary electron which is caught by a collector 5. When supplying the air containing NO and the oxygen containing ozone into said through-hole 15 of such photoelectric multiplier tube 1, and mixing, the light is emitted at the through-hole 15 and provided through paths a1Wa3 onto the photoelectric face 2 quite efficiently while the emitted photoelectron is provided through paths b1Wb3 to the diodes 31W34, 4.