An ultrasonic, flow measuring device, including a measuring tube a transmitter a receiver and at least a first reflection surface. An acoustic signal incident on a first reflection surface and an acoustic signal reflected on the first reflection surface travel, in each case, along a straight subsection of the first signal path. The transmitter, the receiver and the first reflection surface are so oriented with respect to one another and arranged in or on the measuring tube that the acoustic signal on the first signal path from the first transmitter to the first receiver is so reflected on the first reflection surface that the sum of all lengths of all subsections as projected on a measuring tube axis, extending in a first plane parallel to the measuring tube axis, and having a predetermined separation other than zero from the measuring tube axis has a predetermined value different from zero.