An accessory apparatus for flowmeters, especially for ultrasonic flowmeters having at least two successively arranged, plate-shaped or disk-shaped flow influencing elements (1, 2) which are provided with recesses and which are located downstream and/or upstream of the flowmeter, the recesses in the flow influencing elements (1, 2) being made and/or the flow influencing elements (1, 2) being arranged such that there is no free line of sight in the flow direction. The recesses in the flow influencing elements (1, 2) of the accessory apparatus are slots (3, 4) which are offset so that no free line of sight exists through the accessory apparatus.
