Context : Present X-ray missions are regularly discovering new X/ \gamma -ray sources .
The identification of the counterparts of these high-energy sources at other wavelengths is important to determine their nature .
In particular , optical observations are an essential tool in the study of X-ray binary populations in our Galaxy .

Aims : The main goal of this work is to determine the properties of the optical counterpart to the INTEGRAL source IGR J06074+2205 , and study its long-term optical variability .
Although its nature as a high-mass X-ray binary has been suggested , little is known about its physical parameters .

Methods : We have been monitoring IGR J06074+2205 since 2006 in the optical band .
We present optical photometric BVRI and spectroscopic observations covering the wavelength band 4000-7000 Å .
The blue spectra allow us to determine the spectral type and luminosity class of the optical companion ; the red spectra , together with the photometric magnitudes , were used to derive the colour excess E ( B - V ) and estimate the distance .

Results : We have carried out the first detailed optical study of the massive component in the high-mass X-ray binary IGR J06074+2205 .
We find that the optical counterpart to IGR J06074+2205 is a V = 12.3 B0.5Ve star located at a distance of \sim 4.5 kpc .
The monitoring of the H \alpha line reveals V/R variability and an overall decline of its equivalent width .
The H \alpha line has been seen to revert from an emission to an absorption profile .
We attribute this variability to global changes in the structure of the Be star ’ s circumstellar disc which eventually led to the complete loss of the disc .
The density perturbation that gives rise to the V/R variability vanishes when the disc becomes too small .

Conclusions :