PROBLEM TO BE SOLVED: To provide a slime preventive method and device which do not exert an adverse influence to the environment and are low in a running cost without allowing a drug to remain. SOLUTION: The slime preventive device is a device to prevent the generation of slime to the pulp white water supplied to a paper machine 1 in a machine process step of papermaking and has an ozonized water supplying device 2 consisting of an ozone generator 21, clean water supplying system 22, ejector 23, ozone dissolving vessel 24, ozonized water piping system 25, ozonized water dispersing nozzle 26, etc., and a hydrogen peroxide supplying device 3. Accordingly, the high-concentration ozonized water and the hydrogen peroxide are added into the pulp white water, by which the suppression of the slime generation by the synergistic effect of the ozone and the hydrogen peroxide at a small hydrogen peroxide amount and a low cost and without the exertion of the adverse influence on the environment, the prevention of paper cutting and the continuous production of the paper are made possible.
