An object of this invention is to improve resistance to heat and to increase a measurable range of a pressure without increasing a cost. In order to attain the object, a first unit arranged near an exhaust gas pipe and a second unit arranged separately from the first unit and connected to the first unit through a connecting pipe are provided, and the first unit has an exhaust gas flow channel from one end of which an exhaust gas is introduced, an orifice part arranged in a midst of the exhaust gas flow channel, a pressure rising check valve of a mechanically operating type that is connected to a downstream side of the orifice part in the exhaust gas flow channel, and a dilution gas flow channel that is connected to a downstream side of the orifice part in the exhaust gas flow channel so that the diluted exhaust gas diluted by the dilution gas is derived from the other end of the exhaust gas flow channel.