In this work a device for measurement at a constant voltage of the basic electric characteristics of high-resistance dielectric materials and products from them – their electric capacitance and resistance – is developed. The principle of work of the device is based on use of transients in connected in sereies elements having electric capacity and resistance. In the electric circuit of the device the mosfet with high entrance resistance is used. Possibilities of practical use of the device for measurement of surface electret potential, for rejection of potentially unreliable condensers, for diagnostics of corrosion of metal under a pro-tective dielectric covering are considered, etc.