Abstract: The present invention concerns a device for measuring the peak flow of a person's exhalation. The device comprises a frame structure which is provided with a mouth piece. Inside the frame structure, a flap is disposed, along with a pointer. A spring of the flap has been disposed in a hollow space in the lower part of the flap, where the spring is not in contact with the exhaled air. The frame structure comprises a frame part and a transparent cover part, whereby the hygienic conditions of the interior of the device can be observed, without any need to open the same.