Rarefied gas flow into a vacuum through short linearly diverging and converging channels has been examined with the direct simulation Monte Carlo method. Solution to the problem has been suggested using complete geometric setup, with quite large areas on inlet and outlet of a model channel in examined geometry. A mass flow rate through the channel and flow field both inside the channel and upstream and downstream have been calculated in a wide range of gas rarefaction. These calculation results are comparable to corresponding data for the channel with constant cross section. A strong impact of channel geometry and gas rarefaction has been proved.