  We have analyzed the NH$_{2}$CHO, HNCO, H$_{2}$CO, and CH$_{3}$CN
($^{13}$CH$_{3}$CN) molecular lines at an angular resolution of $\sim 0.3''$
obtained by the Atacama Large Millimeter/submillimeter Array (ALMA) Band 6
toward 30 high-mass star-forming regions. The NH$_{2}$CHO emission has been
detected in 23 regions, while the other species have been detected toward 29
regions. A total of 44 hot molecular cores (HMCs) have been identified using
the moment 0 maps of the CH$_{3}$CN line. The fractional abundances of the four
species have been derived at each HMC. In order to investigate pure chemical
relationships, we have conducted a partial correlation test to exclude the
effect of temperature. Strong positive correlations between NH$_{2}$CHO and
HNCO ($\rho=0.89$) and between NH$_{2}$CHO and H$_{2}$CO (0.84) have been
found. These strong correlations indicate their direct chemical links;
dual-cyclic hydrogen addition and abstraction reactions between HNCO and
NH$_{2}$CHO and gas-phase formation of NH$_{2}$CHO from H$_{2}$CO. Chemical
models including these reactions can reproduce the observed abundances in our
target sources.
