In this study, we investigated the optical properties of the Fabry–Pérot (FP) microcavity structure using wire grid (WG) mirrors containing an electrical split–ring resonators (eSRR) or tilted cut wire (CW) metamaterial in the THz region. We designed the metamaterial samples by using the finite difference time domain method and then fabricated them via photolithography. Particularly in the case of the eSRR, which has a more complicated structure than the CW, we have succeeded in preparing the desired sample by adjusting the exposure amount. We measured the transmission spectrum of the fabricated samples by THz time domain spectroscopy. Finally, we observed a large splitting of the transmission peak owing to mode coupling between the light mode of the FP microcavity and the LC electrical resonance of the eSRR. We also found that in the case of the tilted CW, the normal mode splitting width can be controlled by changing the angle between the polarization direction of the incident THz wave and the long axis of the CW.