Abstract: In the general mode, the pressure sensor is communicated with an intake pipe through the first diverged tube by the directional valve so that the sensor can measure the pressure in the intake pipe. Also, in the evapo-purge mode, the pressure sensor is communicated with the purge line through the second diverged tube by the directional valve so that the sensor can measure pressures in the purge line produced when the purge control valve is closed and open. That is, the pressure sensor for measuring a pressure in the purge line is also adapted for measuring the pressure in the intake pipe of the engine. Also, a predetermined range of the difference between the pressures can be settled depending on the load of the engine, such as an engine speed, an intake pipe negative pressure, a throttle opening, and a fundamental injection pulse duration.