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• Lyman- α line coming from the edge LHD plasma is polarized. • Polarization degree of the order of 0.03 has been clearly observed. • Polarization direction is found to be related to the magnetic field direction. • Anisotropic electron velocity distribution function at inboard side causes polarization. Polarization in the Lyman- α line caused by anisotropic electron collisions has been investigated in the Large Helical Device (LHD). High-sensitivity polarization-resolved measurements of the Lyman- α line from edge LHD plasma have been carried out. To obtain spectra of linearly polarized light at all angles a high-reflectivity mirror, a polarization analyzer, and a half-waveplate have been additionally installed into an existing VUV spectrometer system. These optical components have been designed and developed by the CLASP (Chromospheric Lyman-Alpha Spectro-Polarimeter) [R Kano et al. ApJL, 839(1):L10, 2017] team. The present measurement has been made during an electron cyclotron heated discharge. Intensity of the Lyman- α line integrated over line profile has been obtained and plotted as a function of time to generate temporal profile of line. The profile shows that intensity of light varies in synchronization with the angle of the observed linearly polarized light, which clearly indicates that the line is polarized. By performing least-squares fitting on the temporal profile, the magnitude of polarization degree has been evaluated to be 0.033 ± 0.004. In addition, phase analysis of the measured intensity variation has been carried out. From this analysis it has been found that the observed polarization in Lyman- α can be attributed to the anisotropic electron velocity distribution function (EVDF) at the inboard side of LHD plasma. The preliminary results of a simulation model code suggest that the value of polarization degree is negative and electron temperature in the perpendicular direction to the magnetic field is higher compared to electron temperature in the parallel direction. Therefore, the final value of polarization degree in Lyman- α is − 0.033 ± 0.004. [ABSTRACT FROM AUTHOR]