  We present a formulation of the compositeness for baryonic resonances in
order to discuss the meson-baryon molecular structure inside the resonances.
For this purpose, we derive a relation between the residue of the scattering
amplitude at the resonance pole position and the two-body wave function of the
resonance in a sophisticated way, and we define the compositeness as the norm
of the two-body wave functions. As applications, we investigate the
compositeness of the $\Delta (1232)$, $N (1535)$, and $N (1650)$ resonances
from precise $\pi N$ scattering amplitudes in a unitarized chiral framework
with the interaction up to the next-to-leading order in chiral perturbation
theory. The $\pi N$ compositeness for the $\Delta (1232)$ resonance is
evaluated in the $\pi N$ single-channel scattering, and we find that the $\pi
N$ component inside $\Delta (1232)$ in the present framework is nonnegligible,
which supports the previous work. On the other hand, the compositeness for the
$N (1535)$ and $N (1650)$ resonances is evaluated in a coupled-channels
approach, resulting that the $\pi N$, $\eta N$, $K \Lambda$ and $K \Sigma$
components are negligible for these resonances.
