RESPACK is a first-principles calculation software for evaluating the interaction parameters of materials. It is able to calculate the maximally localized Wannier functions, the RPA response functions, and frequency-dependent electronic interaction parameters. RESPACK receives its input data from a band calculation using norm-conserving pseudopotentials with plane-wave basis sets. Utilities which convert a result of xTAPP or Quantum ESPRESSO to an input for RESPACK are prepared. The software has been used successfully for a wide range of materials such as metals, semiconductors, transition-metal compounds, and organic compounds. It supports OpenMP / MPI parallelization.