We have developed the spirometer system; many patients having weak respiration have difficulties in using conventional spirometers in hospitals, because their weak breath can be affected by the errors of inertia and instrumental pressure. We have developed a new ultrasound spirometer using an ARM 920T processor. To detect weak respiratory signals, we add a comparator circuit, which can afford more information of respiration characteristics such as respiration volume, directions, and velocities. We have also developed Gill for graphical display of respiration characteristics. Through the pilot test, it has been verified that the developed spirometer is operating reliably.