The present invention provides a collet capable of efficiently supplying a cooling fluid such as a cutting fluid to a tool and thereby realizing satisfactory cooling by adjusting the flow velocity of the cooling fluid according to the diameter of the tool held by the collet. The collet comprises: a collet body for inserting the shank of the tool, a slot formed at least from the tool insertion side, and a weir member inserted into the slot. The weir member extends from a position recessed from the inner surface of the collet body in a direction closer to the outer surface of the collet body and reaches the outer surface thereof, and a gap S through which the fluid can flow is formed between the weir member and the inner surface of the collet body.