To study adsorption processes on electrode surface,low-noise electrochemical quartz-crystal microbalance (EQCM), of which oscillator is op-amp relaxation type, was made through a lot of trial and errors. The adsorption process is fundamental and plays central role in electrochemistry. But the quantitative investigation had not almost carried out until middle 1980‘s. With the advent of EQCM at that time, active studies have been carried out. As much as fundamental, the adsorption process between electrode and electrolyte is difficult to study. So, very low noisy EQCM and pure chemicals are necessary. In this thesis, underpotential deposition of lead, of which chemistry had been known well, was investigated. Rigorous Ar-bubbling control is essential because the irreducible redox reaction of the dissolved oxygen is not negligible. The catalytic effect of lead on reduction of the dissolved oxygen was verified. A strange reduction peak during oxidative scanning was also appeared, maybe caused by reducible reduction of the dissolved oxygen in the quasiequilibrium state. Also the slight upper shift of current-potential curve or mismatching between current curve in cyclic voltammogram and that estimated from EQCM data in the range of bulk deposition might be attributable to the same reason. For more severe identifying, more of less qualitative technique such as impedance analysis is required.