I downloaded Graphviz 2.38 MSI version and installed under folder C:\\Python34, then I run pip install Graphviz, everything went well.
Graphviz 2.38
C:\\Python34
pip install Graphviz
import os os.environ["PATH"] += os.pathsep + 'D:/Program Files (x86)/Graphviz2.38/bin/'
In windows just add these 2 lines in the beginning, where 'D:/Program Files (x86)/Graphviz2.38/bin/' is replaced by the address of where your bin file is.
That solves the problem.