Inflation in the five-dimensional universe with an orbifold extra dimension

New inflationary solutions to the Einstein equation are explicitly constructed in a simple five-dimensional model with an orbifold extra dimension $S^1/Z_2$. We consider inflation caused by cosmological constants for the five-dimensional bulk and the four-dimensional boundaries. In our solutions the extra dimension is static, and the background metric has a non-trivial configuration in the extra dimension. In addition to the solution for a vanishing bulk cosmological constant, which has already been discussed, we obtain solutions for a non-zero one.