A slide-type writing instrument having a drying-prevention device includes: a pen housing (10); an ink holder (30) disposed in the pen housing (10); a sealing member (40) configured to prevent a drying phenomenon of ink on a pen tip (31); a spring (50) configured to effect elastic support between the sealing member (40) and the ink holder (30); a guide member (60) configured to guide the sealing member (40) when the ink holder (30) is advanced or retreated; and a cam protrusion (70) configured to be responsible for a guiding function of moving the guide member (60). The sealing member includes a soft tube formed of a soft material and a hard tube formed of a hard material and in the shape of a hollow tube to externally surround the soft tube, and the soft tube and the hard tube form a dual cross-section structure.