A V-band coaxial relativistic transit-time oscillator (TTO) with shallow corrugated output structure operating in TM<sub>02</sub> mode is presented. Compared with the deep corrugated output structure, the power handling capacity of the device with shallow corrugated output structure is higher. In particle-in-cell (PIC) simulation, a 403 MW output microwave at 59.10 GHz is obtained with beam voltage of 400 kV, beam current of 5.0 kA under the guiding magnetic field of 1.0 T. The maximum surface electric field in the device is 1.8 MV/cm. Compared with the maximum surface electric field in deep corrugated devices, the maximum surface electric field decreases by 38%. In experiment, a microwave output with power of 258 MW, frequency of 59.04 GHz and pulse duration of 16.0 ns is obtained with diode voltage of 410 kV and beam current of 5.1 kA. The microwave output power and pulse width are significantly improved compared with the previous deep corrugated structure.