PURPOSE: To reduce the error made by an unacountable amount of oil by a method wherein, at the start of oil feeding, if a first change in flow amount pulse signal is fall (rise), only a change in the fall (rise) is thereafter counted and the resulting counted value is displayed as the feed amount of oil.

CONSTITUTION: When an oil feed nozzle 30 is removed from a nozzle case 31, a counting circuit 34 is reset by a nozzle detecting signal s10 to return a display on an indicator 32 to zero and a pump motor is driven by a motor driving circuit 35 to start oil feeding. At this time, a flow amount pulse signal s30 is produced from a flow amount pulse generator 36 provided on a flow meter 27 and, when the nozzle detecting signal s10 is switched from L to H, a selecting means 40 selects the reverse or regular flow depending upon whether the pulse signal s30 is H or L. At the first fall (rise) of the pulse signal s30 delivered through the selecting means 40, the counting action is started and the feed amount of oil corresponding to the counted value is displayed on the indicator 32.