When a SET receives a positioning service from a V-SLP by performing a roaming from a H-SLP to the V-SLP in a SUPL-based positioning system, only a new TLS connection is generated using an abbreviated handshake protocol without generating a new TLS session after the roaming. That is, when opening a TLS session for ensuring security in a SUPL-based positioning method, in particular, when opening a new TLS session between the V-SLP (V-SPC) and the SET after opening the TLS session between the H-SLP and the SET, the key information having used in the previous TLS session is provided to the V-SLP to set a new TLS connection, thereby reducing a load of an entire system.