SS-520-2 sounding rocket flew through the dayside high-latitude auroral region in the vicinity of the cusp. One of the science instruments LEP-ESA/ISA simultaneously observed electron acceleration and ion deceleration when inverted-V type electron precipitations were observed. The correspondence between the electron acceleration energy and the ion deceleration energy clearly indicated the existence of the quasi-static field-aligned potential drop above the sounding rocket. Moreover, ion deceleration started 9.5 seconds later than electron acceleration. By considering a simple temporal model that field-aligned potential drop gradually grew in 10 seconds at 4200 km altitude region, we have succeeded in explaining the observed characteristics of the electron acceleration and ion deceleration.