A coolant supply device includes a coolant tank having first and second coolant reservoirs arranged in parallel with a predetermined space therebetween and a communicating part arranged between the first and second coolant reservoirs to allow them to communicate with each other, and formed to have a U-shaped overall shape. The coolant supply device further includes pumps pumping up coolant from the second coolant reservoir and supplying the coolant to predetermined destinations. The coolant supplied by the pumps is returned to the first coolant reservoir and flows into the second coolant reservoir through the communicating part. The first coolant reservoir has a first agitating nozzle body disposed therein for discharging coolant to assist a flow of coolant flowing toward the communicating part, and the second coolant reservoir has a second agitating nozzle body disposed therein for discharging coolant to assist a flow of coolant flowing therein from the communicating part.