\documentclass[border=2pt]{standalone}
\usepackage{tikz}
\usetikzlibrary{positioning}
\begin{document}
\begin{tikzpicture}[node distance=1.5cm, block/.style={rectangle, draw, minimum width=2cm}]
  \node[block] (A) {Input};
  \node[block, right of=A] (B) {Process};
  \node[block, right of=B] (C) {Output};
  \draw[->] (A) -- (B);
  \draw[->] (B) -- (C);
\end{tikzpicture}
\end{document}
