  With the framework of KIDS (Korea-IBS-Daegu-SKKU) density functional model,
the isoscalar and isovector effective masses of nucleon and the effect of
symmetry energy in nuclear medium are investigated in inclusive $(e,e')$
reaction in quasielastic region. The effective masses are varied in the range
$(0.7 \sim 1.0)M$ with free nucleon mass $M$, and the symmetry energy is varied
within the uncertainty allowed by nuclear data and neutron star observation.
The wave functions of nucleons inside target nucleus are generated by solving
Hartree-Fock equation with adjusting equation of state, binding energy and
radius of various stable nuclei, and effective mass of nucleon in the KIDS
model. With the obtained wave functions, we calculate the differential cross
section for the inclusive $(e,e')$ reaction and compare the theoretical results
with Bates, Saclay, and SLAC experimental data. Our model describes
experimental data better at SLAC-type high incident electron energy than those
measured from Bates and Saclay. The influence of the effective mass and
symmetry energy appears to be precise on the longitudinal cross section.
