To provide a rotation unwinding type writing instrument for preventing as much as possible the breakage of the front end of a cam channel of a rotor and/or a protrusion of a slider even in the case the over torque is applied to the slider.

A rotor 4 is fitted to revolve freely on a cam cylinder 2, and a slider 6 is fitted to slide freely on the rotor, and an engaging protrusion 10 of the slider is slid by a cam channel of the rotor to unwind a writing instrument. In that case, a protrusion 23 is formed on the rear end of the cam cylinder, and a step is formed on the rear of the rotor, or the protrusion is formed on the rear of the rotor, and when the step is formed on the rear of the cam cylinder and the rotor is rotated and a pen point at the refill tip provided continuously to the slider is in the protruded state, the above-said protrusion is engaged with the step.