Intensification of electrons escaping from an intense laser-produced plasma is demonstrated by using double femtosecond laser pulses. The electron density distribution at the rear surface of a laser-irradiated foil target is controlled by preirradiation to suppress sheath field growth and to expand the plasma into which the fast electrons are released. Consequently, the number of electrons escaping from the plasma that have an energy of 380 keV increases by a factor of 7. The experimental results are well explained by numerical simulations of a foil plasma with a preformed plasma and analytical evaluations considering the plasma expansion.