The method for in-situ measurements of the effective pumping speed of high vacuum pumps and the sensitivity of ionization gauges has been developed. The measurement system consists of the gas introduction device with the standard conductance element, and the pumping system with the conductance modulation method. The effective pumping speed of turbomolecular pump, the inverse of the correction factor of ionization gauges, and the effective accommodation coefficient of the spinning rotor gauge were measured by using fifteen kinds of gas species including water vapor. The uncertainty of the measurement was evaluated to be around ten percent. The obtained results are consistent with the conventional literature values within the measurement uncertainties.