Gas system of biogas plant consists of biogas conditioning system and underground gas pipeline system that transport biogas from digester to co-generator or biogas treatment system. Biogas conditioning systems comprises locking devices, safety systems and condensate collector. Biogas temperature and humidity reduction is performed by underground gas pipelines, calculated for a certain length. Condensate is collected to condensate well and then pumped to lagoon or to mobile cistern. Gas pipelines are made of polyethylene pipes, locking device are also underground and do not require any service. Locking device lever is made on the surface. Safety devices are installed on digesters and serve to warn in case of excessive pressure in gas holder or gas pipeline. Sulphur is removed from biogas at gas conditioning system by means of addition of precise air portion into the digester.