[en] Radioactivity monitors installed in National Laboratory for High Energy Physics (KEK) are gas monitors (BLU), dust monitors (BRN), and water monitors (VLT). Description of each type of activity monitors is given. The calibration of gas and water monitors was carried out by using a known amount of standard radionuclides. The calibration of dust monitors was made with a disc-loaded standard source whose activity was known. The graphs to convert ratemeter readings into corresponding activity concentration in air and in water are given. (auth.)