We have measured probabilities with which pions are captured by hydrogen in binary gas mixtures of H 2 + N 2 and H 2 + CO, by using a target chamber with a thin wall and Cherenkov detectors made of new-type lead glass. The chamber had an effective capacity of 320 cm 3 and stood for pressure of 100 kg/cm 2. A disk-shaped CaF 2(Eu) scintillator and a cup-type plastic scintillator were installed in the chamber for detecting the pions stopped in the gas. Both scintillators were viewed by one photomultiplier and their pulses were discriminated by the respective rise times. The measured probability for the H 2 + CO mixture is about 1.5 times as high as that for H 2 + N 2. This fact attests to the importance of the molecular-structure effect on the pion capture process.