A catheter assembly includes a hollow catheter; a catheter hub to which the catheter is fixed; an inner needle including a needle tip, the inner needle being detachably disposed inside of the catheter; a needle hub to which the inner needle is fixed; a catheter operation member configured to move the catheter relative to the inner needle; and a support member disposed at the needle hub. The support member includes a support main body portion that is movable between (i) a first position located on a side of the catheter opposite the catheter operation member, at which the catheter is interposed between the support member and the catheter operation member, and the support main body portion contacts and supports the catheter, and (ii) a second position that is a different position from the first position, at which the support main body portion does not contact the catheter.