The behaviour of the relatively strong absorption line He І λ 587.6 nm with time in spectra of the rapid irregular variable star WW Vul (sp A3) is investigated. In all, 76 spectra were obtained at the 2.6-m ZTSh of the Crimean AO using the low-resolution spectrograph SPEM (R ~ 3000). It is found that both night-averaged and fast changes in equivalent widths W_a of the He І λ 587.6 nm line with a characteristic time of some dozen minutes are present. As absolute energy distribution standards were concomitantly observed, there was the possibility to calculate monochromatic magnitudes of the WW Vul at a wavelength of 550 nm. The night-averaged values of the W_a of the He І λ 587.6 nm line seem to be independent of monochromatic star‘s brightness. The blue-shifted emission component of He I absorption line sometimes arises, being very poor identified. The H_β absorption line profile was used to confirm the spectral type A3 of the WW Vul star.