We report the results of 12 years of observations on the radial velocity variation of the 2.3-μm (4330 cm⁻¹) carbon monoxide absorption lines (first overtone vibration-rotation 2-0 band, R18–R31) of α Orionis (Betelgeuse, M1-2Ia-Iab) using a Fourier transform spectrometer located in the coudé room of the Okayama Astrophysical Observatory's 1.88-m telescope. The mean radial velocity and peak-to-peak amplitude were estimated as 24 km s⁻¹ and 7 km s⁻¹, respectively. However, the variation period could not be determined because the observational frequency data was insufficient.

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