NOVELTY - The device for producing biogas from organic substances, comprises a biogas reactor (210) forming a chamber (232) and supplying a defined mixture of fresh substrate and recirculated product having organic substances over a mixing unit (286), and a controller to determine the weight percentage of the corresponding components of the fresh substrate and to control a supply of the recirculated product and/or the fresh substrate to the mixing unit in dependent of the size correlating with a fresh substrate composition of the fresh substrate supplied to the mixing unit based on the determination.    USE - Device for producing biogas from organic substances.    ADVANTAGE - The device is capable of economically and highly producing the biogas with less energy consumption.    DETAILED DESCRIPTION - The device for producing biogas from organic substances, comprises a biogas reactor (210) forming a chamber (232) and supplying a defined mixture of fresh substrate and recirculated product having organic substances over a mixing unit (286), and a controller to determine the weight percentage of the corresponding components of the fresh substrate and to control a supply of the recirculated product and/or the fresh substrate to the mixing unit in dependent of the size correlating with a fresh substrate composition of the fresh substrate supplied to the mixing unit based on the determination to obtain the defined mixture, so that carbon/nitrogen ratio of 20:1 and pH value of larger than 7 adjust themselves in the defined mixture. The fresh substrate has 22% of dry substance content before reaching the mixing unit and comprises straw chaff (7 wt.%) and cattle liquid manure/solid dung (93 wt.%) or straw chaff (15 wt.%) and cattle liquid manure/solid dung (85 wt.%). An INDEPENDENT CLAIM is included for a method for producing biogas from organic substances by a biogas plant.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic representation of a device for producing biogas from organic substances.    Biogas reactor (210)    Chamber (232)    Mixing unit (286)    Heat exchanger (288)    Temperature sensor. (290)