To allow application to a grinding lubricant formed of a water-soluble dispersion medium having low moisture content and a water-insoluble dispersion medium.

This moisture adjusting device is constituted to recover an abrasive grain-containing grinding lubricant used in grinding work by means of a wire was, a band saw, or water jet and to adjust the moisture of the grinding lubricant in adjustment for recycle. This moisture adjusting device is provided with a storage tank 11 for temporarily storing the recovered grinding lubricant, a moisture make-up means 13 for supplying water in the storage tank, and a moisture content monitoring means 12 installed in the storage tank 11 and capable of calculating the moisture content in the grinding lubricant by measuring the electrostatic capacity of the grinding lubricant in the storage tank 11. The moisture content monitoring means 12 detects the moisture content in the grinding lubricant. The moisture make-up means 13 supplies moisture to the grinding lubricant to adjust the moisture content of the grinding lubricant.