  Cosmological evolution of axionic strings is investigated by numerically
solving field equations of a complex scalar field in 3+1 dimensions. It is
shown that the global strings relax to the scaling solution with a
significantly smaller number density than the case of local strings. The power
spectrum of axions radiated from them is calculated from the simulation data,
which is found to be highly peaked around the Hubble scale, and a more accurate
constraint on the Peccei-Quinn breaking scale is obtained.
