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 and configured to rotate about a rotation axis orthogonal to a longitudinal direction of the assembly. The support member includes a support main body portion that projects in a direction orthogonal to the rotation axis of the support member and that is movable relative to the needle hub between (i) a first position at which the support main body portion contacts and supports the catheter, and (ii) a second position at which the support main body portion does not contact the catheter.