  We explain a method to find internal quark configurations of exotic hadron
candidates by using the constituent counting rule. The counting rule was
theoretically predicted in perturbative QCD for hard exclusive hadron
reactions, and it has been tested in experiments for stable hadrons including
compound systems of hadrons such as the deuteron, $^3$H, and $^3$He. It
indicates that the cross section scales as $d\sigma /dt \sim 1/s^{n-2}$, where
$s$ is the center-of-mass energy squared and $n$ is the total number of
constituents. We apply this method for finding internal configurations of
exotic hadron candidates, especially $\Lambda (1405)$. There is a possibility
that $\Lambda (1405)$ could be five-quark state or a $\bar K N$ molecule, and
scaling properties should be different between the ordinary three-quark state
or five-quark one. We predict such a difference in $\pi^- + p \to K^0 + \Lambda
(1405)$, and it could be experimentally tested, for example, at J-PARC. On the
other hand, there are already measurements for $\gamma + p \to K^+ + \Lambda
(1405)$ as well as the ground $\Lambda$ in photoproduction reactions. Analyzing
such data, we found an interesting indication that $\Lambda (1405)$ looks like
a five-quark state at medium energies and a three-quark one at high energies.
However, accurate higher-energy measurements are necessary for drawing a solid
conclusion, and it should be done at JLab by using the updated 12 GeV electron
beam. Furthermore, we discuss studies of exotic hadron candidates, such as $f_0
(980)$ and $a_0 (980)$, in electron-positron annihilation by using generalized
distribution amplitudes and the counting rule. These studies should be possible
as a KEKB experiment.
