THz technologies are attractive from the viewpoints of material characterization, sensing, imaging, and high-speed communication. For further expansion of applications, the development of novel optics based on metamaterials is crucial. Here, we introduce the recent development of such simple metamaterial optics as a polarizer, a band-pass filter, and an achromatic wave plate in which the metallic structures of several tens μm cause functional optical responses. They have advantages of usability, tunability, easy design, and cost.