A ballpoint pen bends at the pen tip, that can be changed by the force applied when writing. Wobbling does not occur, and a stable writing feel can be obtained. The ballpoint pen makes it possible to clearly change the thickness of the drawn line by the force applied when writing, so that lines of different thickness can be written with a single writing tip using the angle of the ballpoint pen tip. The ballpoint pen includes: a writing ball; a holder for holding the writing ball; an ink supply section; a shaft body inside which the ink supply section is held; and a tip shaft, which is connected to the tip of the shaft body and from which the holder protrudes during writing. The tip shaft is formed by two-color molding in which a front half and a back half are interdigitated in a saw tooth form.

A pressure fluctuation buffering mechanism includes a buffer space connected to a brush via a paint flow space (a paint tank and a paint feeder) through which paint flows. The pressure fluctuation buffering mechanism buffers pressure fluctuations in the paint tank by the flow of paint and air between the paint flow space and the buffer space. The pressure fluctuation buffering mechanism includes a first buffer space forming member for forming a first buffer space in the buffer space, and a second buffer space forming member for forming a second buffer space in the buffer space. The paint between the first buffer space and the paint flow space flows more easily than the paint between the second buffer space and the paint flow space.

Provided are: a ballpoint pen with which the amount of bending of the pen tip can be changed, wobbling does not occur, and a stable writing feel can be obtained; and a ballpoint pen with which, to make it possible to clearly change the thickness of the drawn line by the force applied when writing, lines of different thickness can be written with a single writing tip using the angle of the ballpoint pen tip. The ballpoint pen is provided with: a writing ball; a holder for holding the writing ball by means of a swaged section the tip of which has been swaged; an ink supply section for supplying ink to the holder; a shaft body inside which the ink supply section is held; and a tip shaft, which is connected to the tip of the shaft body and from which the holder protrudes during writing.

A ballpoint pen 10 includes: a ballpoint pen tip 20 having a writing ball 30 and a holder 21 holding the writing ball 30; a shaft tube 12 to which the rear end part of the ballpoint pen tip 20 is mounted; and ink 40 accommodated in the shaft tube 12. The holder 21 has an ink guiding hole 26 formed from the rear end thereof toward the head end thereof and a ball house 22 formed with the inner circumference near the head end of the holder 21 expanded. The writing ball 30 is formed of a zirconia sintered body with the content of an aluminum element being less than 0.1 weight %, and the ink 40 contains inorganic particles 41.