A Bernstein wave propagating obliquely to the magnetic field is excited by a coaxial antenna in a streaming plasma and detected by an interferometer system, which shows that the dispersion relation for the wave is consistent with the theoretical result. Another wavelike signal with a shorter ``wavelength'' is observed downstream only of the exciting antenna, and its ``phase velocity'' is approximately equal to the velocity of the plasma stream calculated from the Doppler shifts of Bernstein waves in both upstream and downstream regions, which may show that the signal does not propagate as the wave but floats down on the plasma stream as the modulation of plasma particles.