A sheet humidifying device includes a pair of humidifying rollers which form a nip portion by pressure contacting against each other and giving water to a sheet passing through the nip portion, a water-supply roller that pressure contacts the humidifying roller and supplies water to the humidifying roller, a water vessel that stores water to be supplied to the water-supply roller, and a pressure-contact releasing section that releases pressure-contact of the pair of humidifying rollers and releases pressure-contact between the humidifying roller and the water-supplying roller.