A catheter assembly includes a catheter, an inner needle, and a deflection suppression mechanism that suppresses a deflection of the inner needle. A side flow path structure having at least one liquid passage is provided on a circumferential wall of the catheter. The deflection suppression mechanism has a sliding contact support portion that can support the catheter while rubbing against the catheter when the catheter is advanced with respect to the inner needle. In an initial state, the sliding contact support portion is located to be closer to a proximal side than a liquid passage located on a most distal side in the side flow path structure.
