  An algorithm for the automatic Feynman diagram (FD) generation is presented
in this paper. The algorithm starts directly from the definition formula of FD,
and is simple in concept and easy for coding. The symmetry factor for each FD
is naturally generated. It is expected to bring convenience for the researchers
who are studying new calculation techniques or making new calculation tools and
for the researchers who are studying effective field theory. A C-program made
from the algorithm is also presented, which is short, fast, yet very general
purpose: it receives arbitrary user defined model and arbitrary process as
input and generates FD's at any order.
