A differential pressure type inflating device, adapted for fast inflating the devices that need inflating, comprises a gas container, a relief valve, a gas nozzle, a pipe joint, a switch valve, and a relief pipe. When external high pressure gas enters the gas container and renders the gas pressures in the gas container and the relief pipe reaching a balance condition, the switch valve can be pressed to generate pressure drop in the relief pipe, which launches the relief valve and discharges the high pressure gas in the gas container from the gas nozzle. In this design, the gas container, relief valve, gas nozzle, relief pipe, and pipe joint are connected with screwing structures, so as to achieve the function of easy assembling.