We have been developing an S-band Cs-Te photocathode rf electron gun system for pulse radiolysis and laser Compton scattering experiment at Waseda University. These researches demand for high quality and well controlled electron beam. In order to measure the ultra-short electron bunch, we decided to use rf-deflector cavity, which can convert the longitudinal distribution to that of transverse. With this technique, the longitudinal bunch profile can be obtained as the transverse profile. We used the 3D electromagnetic simulation codes HFSS for designing rf-deflector cavity and GPT for beam tracking. The cavity has 2 cell structures operating on p mode, standing wave, dipole (TM 120) mode at 2856 MHz. We have confirmed on HFSS that 2 cell rf-deflector cavity can produce 660 G magnetic field per cell on beam line with 750 kW input rf power. This field strength is equivalent with our target, which is 100 fs bunch length measurement at 4.3 MeV. In this conference, we will present the cavity structure design, the present progresses and future plan.