To provide a cap-type writing utensil which can inhibit the contact of a cap opening end with a barrel and thereby, prevent the appearance of the writing utensil from being impaired, when the cap is fitted to the tip of the barrel or fitted back through the rear of the barrel during the use of the writing utensil.

This cap-type writing utensil has a mouthpiece and a tail plug fitted to both ends of the barrel and besides, a cap which can be fitted in place at both ends of the barrel. In addition, the maximum outside diameter part A of the mouthpiece and the minimum outside diameter part B near the adjacent part to the mouthpiece of the barrel are in the relationship of A>B, and the maximum outside diameter part C of the tail plug and the minimum outside diameter part D near the adjacent part to the tail plug of the barrel, are in the relationship of C>D. The inner peripheral surface of the opening end part of the cap is bevelled.