The vacuum electrical breakdown characteristics of oxygen-free copper electrodes, which were processed by precision diamond turning machining in a clean room and were heat-treated in hydrogen after that machining, were investigated by applying impulse voltage. These electrodes were carried in mobile vacuum chamber in order to keep them clean. The surface conditions were analyzed by the X-ray Photoelectron Spectroscopy (XPS) before and after the ion-beam sputtering and after the 500 times repetitive breakdowns. These experiments can be performed in in-situ experimental apparatus that are maintained in ultra-high vacuum (10^-7 to 10^-8Pa). As a result, these electrodes showed higher breakdown fields at the first breakdown relative to values obtained in the past studies. In addition, their conditioning achieved with less number of breakdowns. According to the XPS spectra, it was confirmed that organic contaminants were reduced by heat treatment in hydrogen and ion beam sputtering. These shows that heat treatment in hydrogen is effective in reducing contaminants on the electrode surface and improving the breakdown characteristics.