The invention relates to a mixing device (6) for thinning a fibrous material suspension (1), suitable for producing a paper, board, tissue or other fibrous material web, by means of a thinning liquid (3), which is arranged after a cleaning device for removing contaminants from the fibrous material suspension (1). Thereby the most simple and comprehensive mixing possible shall be enabled such that the purified fibrous material suspension (1) is conducted via at least one suspension nozzle (11) into a mixing container (14) having an outlet (13), into which the thinning liquid (3) is also conducted via at least one thinning nozzle (12).
