An oil supply apparatus for use with copying machines comprises a tank for holding an offset preventing oil therein, a pump for sucking the oil from the tank, a container for holding the sucked oil therein, an oil application device for applying the oil taken from the container to an image fixing roller and an oil recovery means device for recovering an excessive amount of the oil which was taken from the container and returning it to the tank. The oil is always circulated in the oil supply apparatus and the container can be detached from the tank. When the container is detached from the tank, a stopper is engaged in a drain hole formed in the container concurrently with the detachment action so as to prevent the oil from being spilled.