Nowadays the project of laser-driven Compton light source started in ILP SB RAS in collaboration with BINP SB RAS. It was expected the production of 1-10 pC electron beams sub-ps time range duration with energies up to 100÷150 MeV as a result of the first stage of the project. It is necessary to have the non-destructive charge detector for on line measurements during experiments. We proposed the detector based on reentrant RF resonator technology. Single circular cylinder geometry of measuring RF cavity is insensitive to electron beam position and size as well as time structure of bunch (on the assumption of sufficiently short bunch). Base data of cavity are close to acceleration section elements of VEPP-5 linac.The prototype of the detector was successfully tested at VEPP-5 electron linac. Measured charge of single bunch reaches down to 1 pC and less. This paper presents the results of development and testing of diagnostics.