A non-trigonometric wave is excited in the LMD-U device. Transition to a turbulent wave from the non-linear wave is made by controlling the strength and the shape of magnetic field and/or neutral pressure. To clarify the turbulence transition mechanism, the two-dimensional structure of the non-linear wave is observed by using the two-point correlation technique. Obtained results under this experimental condition are as follows: 1) The waveforms of Ĩis and Ṽf,up/down are similar to sawtooth waves and the PDFs are skewed. 2) The largest spectral peak is excited at 1.2kHz and the even and odd higher harmonic waves are also excited. 3) The coherence structure at 1.2kHz is broad both in the azimuthal and the radial directions. 4) A spiral-shaped (m = 1) wave is formed.