An expiration suction passage communicating with an expiration blowing part provided with a non-airtight mask is connected to a forward end surface of a syringe through a two-way on-off electromagnetic valve, while an expiration transmission passage communicating with a sample outlet is also connected to the forward end surface of the syringe. A two-way on-off electromagnetic valve is provided in the expiration transmission passage, and an O.sub.2 sensor is provided between the electromagnetic valve and the sample outlet as a standard gas sensor. The syringe has a capacity capable of collecting several breaths, and a sucking operation is driven at a speed for collecting several breaths in single suction.