An ultrasonic flow measurement device for ascertaining flow velocity, respectively volume flow, of a fluid, especially a gas or a liquid, using a travel-time difference method, comprising: a measuring tube having a straight measuring tube axis; at least one transmitter for transmitting an acoustic signal; at least one receiver for receiving the acoustic signal; and at least one reflection surface for reflecting the acoustic signal. The transmitter and the receiver are arranged on the tube wall of the measuring tube in such a manner that they can transmit the acoustic signal inclined or perpendicularly to the flow direction of the fluid, wherein at least one reflection surface is embodied concavely in a preferential direction; and a method for ascertaining flow velocity, respectively volume flow, of a fluid.