Disclosed is a pen adapted to be pressurized and capable of being manufactured with low cost, with which ink can be smoothly supplied and an excessive pressurization within an ink accommodating tube and the leakage of ink can be prevented, as well as a pen can be easily used in a state that a pen tip is directed upwardly. The pen comprises a pressurizing pump mechanism 10 which pressurizes an inside of ink accommodating tube 3 and includes a pressurizing chamber 14 communicating with the inside of the ink accommodating tube, an elastic spherical body 16 disposed to be pushed into the pressurizing chamber, a compression spring 17 that urges the spherical body in a direction to be released from within the pressurizing chamber, and a pressing stem 18 that moves forcedly the spherical body towards the front against the urging force of the compression spring to be pushed into the pressurizing chamber in an airtight state; the inside of the ink accommodating tube is pressurized by the operation of the pressing stem to push the spherical body into the pressurizing chamber against the urging force of the compression spring; and the spherical body is released from within the pressurizing chamber by the urging force of the compression spring in accordance with the pushing-release operation of the pressing stem to maintain the inside of the ink accommodating tube in a state ventilates with ambient air.