Context : Sun-like stars are promising candidates to host exoplanets and are often included in exoplanet surveys by radial velocity ( RV ) and direct imaging . In this paper we report on the detection of a stellar companion to the nearby solar-analogue star HD 104304 , which previously was considered to host a planetary mass or brown dwarf companion . Aims : We searched for close stellar and substellar companions around extrasolar planet host stars with high angular resolution imaging to characterize planet formation environments . Methods : The detection of the stellar companion was achieved by high angular resolution measurements , using the “ Lucky Imaging ” technique at the ESO NTT 3.5m with the AstraLux Sur instrument . We combined the results with VLT/NACO archive data , where the companion could also be detected . The results were compared to precise RV measurements of HD 104304 , obtained at the Lick and Keck observatories from 2001-2010 . Results : We confirmed common proper motion of the binary system . A spectral type of M4V of the companion and a mass of 0.21 M _ { \odot } was derived . Due to comparison of the data with RV measurements of the unconfirmed planet candidate listed in the Extrasolar Planets Encyclopaedia , we suggest that the discovered companion is the origin of the RV trend and that the inclination of the orbit of i \approx 35 \degr explains the relatively small RV signal . Conclusions :