A catheter assembly includes a catheter, a catheter hub fixed to the proximal end of the catheter, a needle positioned inside the catheter, a gripping member connected to a proximal portion of the inner needle, a catheter operating member connected to the catheter hub and movable in the longitudinal direction relative to the inner needle, a guide wire slidably positioned in the inner needle and possessing a length longer than both the inner needle and the catheter, and a wire operating member connected to the guide wire so that movement of the wire operating member results in movement of the guide wire. The catheter operating member is configured to press a portion of the catheter between the proximal end of the catheter and the distal end of the catheter when the user presses on the catheter operating member while puncturing a living body with the needlepoint.