The order parameter Φ of the four-dimensional simple hypercubic spin-1/2 Ising ferromagnet is calculated by the Monte Carlo technique. The data, which may be represented by Φ(t)=B(-t)12|ln(-t)|13 with 1.53<B<1.56 for 0.005<-t(Tc-T)Tc<0.40, supports the theoretical prediction of a multiplicative logarithmic correction to the mean-field description of the critical behavior in four dimensions.