This study investigates the institution of public security and its structure in the period of the Prophet Muhammad and the first-four Caliphs. This institution concerns the judicial events in society. There was not any institution of security in the Jahiliyya period because the Arabs at that time were not in need of it. In the period of the Prophet Muhammad, the activities of security completely consist of the protection of Prophet and Medina. The guards of this period are named “Haras” and “Asas”. In the period of the first-four Caliphs, this institution generally appears as “Shurta” and “Ahdath” and “Meuna” and “Jilvaz” rarely in addition to “Haras” and “Asas”. This organization was formed first in the period of Caliph Umar and developed in the time of Caliph Uthman. In this period, the institution performed whole activities of contemporary institution of police force