\documentclass{article}

\usepackage{tikz}
\usetikzlibrary{arrows,shapes,automata,backgrounds,petri}
\usepackage[utf8]{inputenc}
\usepackage[french]{babel}
\usepackage{ccicons}

\begin{document}





\begin{center}
\begin{tikzpicture}[node distance=24mm,bend angle=45,auto]
  \tikzstyle{place}=[circle,thick,draw=blue!75,fill=blue!20,minimum size=8mm]
  \tikzstyle{transition}=[rectangle,thick,draw=red!75,
  			  fill=red!20,minimum size=4mm]
    \node [place] (a) {};
    \node [transition] (r1) [below of=a]{};
    \node [place, below left of=r1] (b) {};
    \node [place, below right of=r1] (c) {};
	\path (a) edge[->, ultra thick] (r1);
	\path (a) edge[->, ultra thick, bend left=30] (r1);
	\path (a) edge[->, ultra thick, bend right=30] (r1);
	\path (r1) edge[->, ultra thick, bend left=30] (b);
	\path (r1) edge[->, ultra thick, bend right=30] (b);
	\path (r1) edge[->, ultra thick] (c);
	\node [transition] (r2) [below of=b] {};
	\node [transition] (r3) [below of=c] {};
	\path (b) edge[->, ultra thick, bend left=45] (r2);
	\path (b) edge[->, ultra thick, bend right=45] (r2);
	\path (b) edge[->, ultra thick, bend left=15] (r2);
	\path (b) edge[->, ultra thick, bend right=15] (r2);
	\path (b) edge[->, ultra thick, bend left=30] (r2);
	\path (b) edge[->, ultra thick, bend right=30] (r2);
	\path (c) edge[->, ultra thick, bend right=30] (r3);
	\path (c) edge[->, ultra thick, bend left=30] (r3);
	\node [place] (d) [below left of=r2] {}; 
	\node [place] (e) [below of=r2] {}; 
	\node [place] (f) [below of=r3] {}; 
	\node [place] (g) [below right of=r3] {}; 
	\path (r2) edge[->, ultra thick] (d);
	\path (r2) edge[->, ultra thick, bend left=30] (d);
	\path (r2) edge[->, ultra thick, bend right=30] (d);
	\path (r2) edge[->, ultra thick, bend left=60] (d);
	\path (r2) edge[->, ultra thick, bend right=60] (d);
	\path (r2) edge[->, ultra thick, bend left=30] (e);
	\path (r3) edge[->, ultra thick, bend right=30] (f);
	\path (r3) edge[->, ultra thick, bend left=30] (g);
\end{tikzpicture}
\end{center}


\end{document} 
