A catheter apparatus includes a replaceable module, a main body portion and a sensing module. The main body portion includes a tube, a urine guide opening and an elastic unit. The replaceable module includes a control unit. A first terminal of the tube is coupled to the replaceable module and a second terminal of the tube is inserted into the bladder. The urine guide opening is disposed at the second terminal of the tube and used to guide urine into the tube when the second terminal of the tube is inserted into the bladder. The elastic unit is disposed at the second terminal of the tube and coupled to the control unit. The sensing module is coupled to the control unit and used to sense whether the second terminal of the tube is inserted to the correct position in the bladder and transmit sensing result to the control unit.