To increase the feed value of a roughage by using a urea adding apparatus.

By using an adding apparatus 6 comprising a urea liquid container 2, a liquid transporting pump 3, a solenoid valve 4 and a spray cylinder 5, which are all placed on an existing roll baler 1 of a working machine forming a cylindrical package of pasture, a 35-40% urea liquid 8 is homogeneously added to pasture straw 7 collected in a stripe of about 1 m in width during collection. The control 9 of spraying the urea liquid 8 is carried out at a driving seat of the existing tractor. After the addition of the urea liquid, the cylindrical package is wrapped and kept in a closed state for 50 days or more in summer or for 120 days or more in winter. By this treatment, the feed value of the pasture straw is increased, and the wrapped material can be transported even during the treatment.