Abstract: A writing instrument case includes a case body, a lid frame releasably attached to the case body, an edge member provided at an opening of the casy body such as to engage with the lid frame, the edge member having a row of through-holes through which writing instruments may be inserted one by one, a retainer plate made of flexible material and provided between the edge member and the case body, the retainer plate having retaining holes aligned with the through-holes, each of the retaining holes having an inner pheriphery on which protrusions are appropriately provided. The case body has a recessed edge on the upper portion of its periphery surface, while the lid frame has a protruding member engaging with the recessed edge.