This Letter demonstrates tailored optical frequency comb (OFC) generation using a LiNbO3 Mach-Zehnder modulator driven by a combination of first- and second-order harmonics of the RF signal. A quasi-rectangular-shaped OFC with less than 1 dB flatness among 11 lines was experimentally obtained when a slight second-order harmonic of the RF signal (0.1 times the half-wavelength voltage) was introduced. Good agreement was obtained between the measured and calculation results for OFCs. We discuss conditions to obtain flat OFCs using this method along with details concerning OFC conversion efficiency and bandwidth.