Process for the oxidation of a hydrocarbon comprising partially oxidizing in a reaction zone, a mixture comprising a hydrocarbon and an oxygen-containing gas in the presence of a catalyst which is capable of supporting oxidation of the hydrocarbon. It is composed mainly of a multitude of micro-volumes installed in a closed space between a lower border, upper border and side border. Watertightness between the universal cable and the case body is maintained at an abutting surface which is orthogonal to the axis thereof, and watertightness between the control cable and the case body is maintained at the outer peripheral surface thereof.