We analyzed time-of-flight (TOF) data from the Arase satellite to investigate temporal variations of O2+, NO+, and N2+ at 19.2 keV/q in the inner magnetosphere for 6.5 years from the solar declining to rising phases. Molecular ion counts were estimated by subtracting the background contamination of oxygen counts. While the number of clear molecular events was small, the estimated molecular ion counts exhibited good correlation with the solar wind dynamic pressure and SYM-H index. Long-term variations of molecular ions were different from that of oxygen ions. Additionally, we discuss the importance of the solar wind dynamic pressure in causing the escape of molecular ions into the magnetosphere through an increase in the convection electric field, which causes different evolutions of oxygen ions and molecular ions.