A slide type writing tool having a dryness prevention unit. The writing tool includes a hollow shaft having at a first end thereof a nib hole. A knock part is inserted into an insert hole formed in a second end of the shaft. A cartridge is inserted into the shaft and is integrated with the knock part. A control module is made of an elastic material, such as rubber, and includes an O-ring part coming into close contact with the nib hole, a spherical door having a spherical surface, a tubular holder secured to the cartridge, a first hinge coupling the O-ring part with the spherical door, and a second hinge integrally coupling the spherical door with the holder. First and second springs are provided in the shaft to act elastic restoring force between the control module and the cartridge.