\documentclass{article}
\usepackage{amsmath,amssymb,pgf,tikz}
\usetikzlibrary{arrows,automata}
\begin{document}

\begin{tikzpicture}[->,>=stealth',shorten >=1pt,auto,node distance=1.5cm,semithick]
  \tikzstyle{every state}=[fill=white,draw=black,text=black,minimum size=1.1cm]

  \node (A) {};
  \node[state] (A2) [right of=A] {$\lambda_1$};
  \node (A3) [right of=A2] {};

  \node (B) [below of=A] {};
  \node[state] (B2) [right of=B] {$\lambda_2$};
  \node (B3) [right of=B2] {};

  \node (C) [below of=B] {};
  \node (C2) [right of=C] {\vdots};
  \node (C3) [right of=C2] {};

  \node (D) [below of=C] {};
  \node[state] (D2) [right of=D] {$\lambda_n$};
  \node (D3) [right of=D2] {};

  \node (S) [left of=C] {start};
  \node (E) [right of=C3] {end};

  \path[-] (A.center) edge node {$p_1$} (A2);
  \path[-] (B.center) edge node {$p_2$} (B2);
  \path[-] (D.center) edge node {$p_n$} (D2);

  \path[-] (A2) edge node {} (A3.center);
  \path[-] (B2) edge node {} (B3.center);
  \path[-] (D2) edge node {} (D3.center);

  \path[-] (A.center) edge node {} (D.center);
  \path[-] (A3.center) edge node {} (D3.center);

  \path (S) edge node {} (C.center);
  \path (C3.center) edge node {} (E);

\end{tikzpicture}
\end{document}