The catheter assembly (10A) includes a needle support portion (20) that supports the inner needle (16) via the catheter (12) on the distal side of the catheter hub (14). The needle support portion (20) includes a pair of support arms (42) that can be opened and closed in the left-right direction, and a restraint portion (44) that can be restrained in a state where the pair of support arms (42) are closed and can be released. And have. The needle hub (18) has an extension part (38) extending in the distal direction from the catheter hub (14), and a connection part between the pair of support arms (42) and the extension part (38) is provided. It exists in the front end side rather than the base end of a catheter hub (14).カテーテル組立体（１０Ａ）は、カテーテルハブ（１４）よりも先端側でカテーテル（１２）を介して内針（１６）を支持する針支持部（２０）を備える。針支持部（２０）は、左右方向に開閉可能な一対の支持アーム（４２）と、一対の支持アーム（４２）を閉じた状態に拘束可能であり且つ拘束を解除可能な拘束部（４４）とを有する。針ハブ（１８）は、カテーテルハブ（１４）よりも先端方向に延出する延出部（３８）を有し、一対の支持アーム（４２）と延出部（３８）との接続部が、カテーテルハブ（１４）の基端よりも先端側にある。
