Cytidine derivative-containing antitumor agent for continuous intravenous administration

To provide a method for administering ECyd to a patient, which realizes a continuous therapy without expressing peripheral neurotoxicity caused by ECyd and which exhibits an excellent therapeutic effect with ensuring prolongation of the survival of the patient. The invention provides an antitumor agent containing ECyd or a salt thereof, which is administered to a cancer patient through continuous intravenous administration at a dose of 1.30 to 8.56 mg/m 2 as reduced to ECyd, for each administration period of 2 to 336 hours.