The retractable container of the present invention includes a body which accommodates a receptor supported by a spring and a knob configured to deploy and retract the receptor. In the retractable container, the body accommodates the receptor and the spring therein, has an entrance formed on one side thereof and an insertion opening formed on the other side thereof, into which the receptor and the knob are inserted, and comprises a body cam integrally formed with the body and comprising a guide bar which extends from the body to be disposed adjacent to a side of the insertion opening, and the knob is configured to have a feature in which a knock operation part is formed integrally with a protrusion member which connects an extension part and a pressing part inserted into the insertion opening of the body, thus the guide bar of the body cam is moved to respond to a change in position of the knock operation part.

A writing instrument part that improves the releasability of a core pin is provided. In a writing instrument part by the insert molding method in which a wooden barrel material made of natural wood flour and a water-soluble resin binder is injected into a mold, the wooden barrel material and a core pin having a paper straw inserted therein are integrated, and a two-layer structure having a paper straw layer as an inner layer and a wooden barrel layer as an outer layer is formed.

An attachment structure in a writing instrument, includes: a first component; and a second component configured to be fitted into a fitting hole provided at an end of the first component, the second component including: a small-diameter portion; and a large-diameter portion disposed in front of the small-diameter portion; and a first outer step portion disposed between the small-diameter portion and the large-diameter portion, the fitting hole including: a small-diameter hole portion; and an inner step portion disposed in front of the small-diameter hole portion, the small-diameter portion being fitted into or loosely fitted into the small-diameter hole portion, the first outer step portion coming into contact with the inner step portion, the small-diameter hole portion includes a barb portion protruding from the inner face of the small-diameter hole portion, the barb portion being deformable by contact with the small-diameter portion when the second component is fitted.

A writing instrument part that improves the releasability of a core pin is provided. In a writing instrument part by the insert molding method in which a wooden barrel material made of natural wood flour and a water-soluble resin binder is injected into a mold, the wooden barrel material and a core pin having a paper straw inserted therein are integrated, and a two-layer structure having a paper straw layer as an inner layer and a wooden barrel layer as an outer layer is formed.

An axial cylinder extending in an axial direction along a center axis and a writing member disposed inside the axial cylinder. The axial cylinder has fiber-like protrusions protruding toward an outside in a radial direction from an outer circumferential surface of the axial cylinder, the plurality of fiber-like protrusions are provided side by side on the outer circumferential surface, and each of the fiber-like protrusions has a plurality of rib parts which extend in predetermined directions when viewed from the outside in the radial direction and which are disposed side by side in a width direction orthogonal to the predetermined directions and a step part which is disposed between rib parts adjacent to each other in the width direction or disposed at an end portion in the width direction of the rib parts and extends in a predetermined direction.