\documentclass[a4paper,12pt]{report} 
\usepackage{tikz,amsmath,amssymb}
\tikzstyle{vertex}=[circle, draw, inner sep=0pt, minimum size=12pt] 
\newcommand{\vertex}{\node[vertex]}
\tikzstyle{vertexs}=[draw,minimum width=.4cm,minimum height=.4cm]
\newcommand{\vertexs}{\node[vertexs]}
\begin{document}
\begin{figure}[htbp]
\[
\begin{tikzpicture}[scale=1,thick,>=stealth] 
\vertex (a1) at (0,0) []{};
\vertexs (b1) at (0,-1) []{};
\vertex (a2) at (-1.2,-2) []{};
\vertex (a3) at (-.6,-2) []{};
\vertex (a4) at (0,-2) []{};
\vertex (a5) at (.6,-2) []{};
\vertex (a6) at (1.2,-2) []{};
\draw [->] (b1) -- (a1);
\draw [->] (a2) -- (b1);
\draw [->] (a3) -- (b1);
\draw [->] (a4) -- (b1);
\draw [->] (a5) -- (b1);
\draw [->] (a6) -- (b1);
\end{tikzpicture}
\]
\caption{\label{fig:sym}گراف}
\end{figure}
\end{document}