To provide a position detection system capable of detecting a position both indoors and outdoors.

In S10, a terminal device 2 recognizes a transmission device discrimination ID from a radio wave transmitted from a transmission device 1, and detects an offset peak time from the power intensity of the radio wave. In S20, information wherein the offset peak time is correlated with the transmission device discrimination ID is generated and recorded in a recording part 24. In S30, the information is transmitted to a server 3. In S40, the server 3 determines position information of the terminal device 2 by using three or more offset peak times, and information showing a position relation of the transmission device 1 held beforehand, or by using the offset peak times, the information showing the position relation of the transmission device 1 held beforehand, and a result acquired by measuring beforehand the offset peak times from the plurality of transmission devices 1. In S50, the server 3 transmits the information to the terminal device 2. In S60, the terminal device 2 receives the position information, and provides the position information to a position information utilization part 25.