A system comprising a coolant supply system and a laser processing head,: wherein the laser processing head comprises: a capacitance type distance sensor for measuring a distance between the laser processing head and a workpiece; and wherein the coolant supply system comprises: a coolant tank for accumulating coolant generated by using deionized water; a coolant supply passage for supplying the coolant, which is accumulated in the coolant tank and to be injected from the laser processing head toward the workpiece, to the laser processing head; an electric conductivity meter for measuring an electric conductivity (σ) of the coolant to be supplied to the laser processing head; and characterized in that the coolant supply system comprises: a drainage passage (9, 6) having an electromagnetic valve (B2, B4) and capable of draining the coolant to an outside from the coolant tank; and a controller configured to control open and close operations of the electromagnetic valve, wherein the controller is configured to turn the electromagnetic valve (B2, B4) from a closed state into an open state to drain the coolant accumulated in the coolant tank through the drainage passage (9, 6) when a measured value of the electric conductivity meter exceeds over a preset upper limit value (σh1). a capacitance type distance sensor for measuring a distance between the laser processing head and a workpiece; and wherein the coolant supply system comprises: a coolant tank for accumulating coolant generated by using deionized water; a coolant supply passage for supplying the coolant, which is accumulated in the coolant tank and to be injected from the laser processing head toward the workpiece, to the laser processing head; an electric conductivity meter for measuring an electric conductivity (σ) of the coolant to be supplied to the laser processing head; and characterized in that the coolant supply system comprises: a drainage passage (9, 6) having an electromagnetic valve (B2, B4) and capable of draining the coolant to an outside from the coolant tank; and a controller configured to control open and close operations of the electromagnetic valve, wherein the controller is configured to turn the electromagnetic valve (B2, B4) from a closed state into an open state to drain the coolant accumulated in the coolant tank through the drainage passage (9, 6) when a measured value of the electric conductivity meter exceeds over a preset upper limit value (σh1). a coolant tank for accumulating coolant generated by using deionized water; a coolant supply passage for supplying the coolant, which is accumulated in the coolant tank and to be injected from the laser processing head toward the workpiece, to the laser processing head; an electric conductivity meter for measuring an electric conductivity (σ) of the coolant to be supplied to the laser processing head; and characterized in that the coolant supply system comprises: a drainage passage (9, 6) having an electromagnetic valve (B2, B4) and capable of draining the coolant to an outside from the coolant tank; and a controller configured to control open and close operations of the electromagnetic valve, wherein the controller is configured to turn the electromagnetic valve (B2, B4) from a closed state into an open state to drain the coolant accumulated in the coolant tank through the drainage passage (9, 6) when a measured value of the electric conductivity meter exceeds over a preset upper limit value (σh1). a drainage passage (9, 6) having an electromagnetic valve (B2, B4) and capable of draining the coolant to an outside from the coolant tank; and a controller configured to control open and close operations of the electromagnetic valve, wherein the controller is configured to turn the electromagnetic valve (B2, B4) from a closed state into an open state to drain the coolant accumulated in the coolant tank through the drainage passage (9, 6) when a measured value of the electric conductivity meter exceeds over a preset upper limit value (σh1).