\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{pgf, tikz}
\usetikzlibrary{arrows , automata , positioning}
\begin{document}
\begin{center}
\begin{tikzpicture}[>=stealth',shorten >=1pt,auto,node distance=2.5cm]
%Knoten
\node (0) [state, thick] {0};
\node (1) [state, thick, right of= 0] {1};
\node (2) [state, thick, above of= 1, right of= 1] {2};
\node (3) [state, thick, above of= 2, right of= 0] {3};
%Verbindungen
\path[thick,->]
(0) edge [bend angle=25, bend left,above] node {0/2} (3)
(0) edge [bend angle=33, bend left,above] node {1/3} (3)
(1) edge [bend angle=35, bend right,above] node {0/2} (0)
(1) edge [loop] node {1/0} (1)
(2) edge [bend angle=45, bend right,above] node {0/0} (1)
(2) edge [loop] node {1/0} (2)
(3) edge [bend angle=55, bend right,above] node {0/3} (2)
(3) edge [bend angle=108, bend left,below] node {1/2} (0)
;
\end{tikzpicture}
\end{center}
\end{document}
