A monopole antenna capable of implementing an MMIO system, which includes a ground part formed of plate metal, a monopole antenna element connected to one side of the ground part and formed of strips bent multiple times, an auxiliary antenna element connected to one side of the ground part and disposed adjacent to the monopole antenna element to electrically connect to the monopole antenna element, and a short-circuit part interconnecting the monopole antenna element and the auxiliary antenna element. Accordingly, the monopole antenna element is bent multiple times so that the antenna can become compact in less than half a width compared to the conventional antenna, and when the MIMO system is constructed, the interference between the respective antennas can be reduced so that the array antenna can become compact in size.