A catheter assembly includes a catheter, a catheter hub fixed to a proximal end portion of the catheter, a hollow inner needle removably located in the catheter and including a distal end portion at which is located a needlepoint to puncture skin of a patient, and a guide wire slidably positioned in the inner needle. The guide wire is longer than both the inner needle and the catheter. A wire operating member is connected to the guide wire and is displaceable in a forward direction relative to the inner needle and the catheter. A main body is detachably connected to the catheter hub and includes a finger-engaging projection at a distal portion of the main body that is engageable by a user's finger to advance the main body and the catheter in the forward direction.