The mechanism of the occurrence of intraatomic diamagnetic currents in the neutral He atoms with microscopic sizes is investigated. It is found that most of all electrons can form electron pairs originating from attractive Coulomb interactions between two electrons with opposite spins occupying the 1s atomic orbital in the neutral He atom at 298 K. Intraatomic diamagnetic currents in the neutral He atoms with microscopic sizes can be explained by such electron pairing. The transition temperature Tc(He),(1s) value at which intraatomic diamagnetic currents can disappear in each He atom is estimated. The Tc(He),(1s) values for the neutral He atoms with microscopic sizes are estimated to be much larger than the superconducting transition temperatures Tc,BCS values for the conventional superconductors with macroscopic sizes. This result can be understood from continuous energy levels of electronic states in conventional superconductivity with macroscopic sizes, and from discrete energy levels of electronic states in the neutral He atoms with microscopic sizes. The energy difference between the occupied and unoccupied orbitals decreases with an increase in material size and thus the second-order perturbation effect becomes more important with an increase in material size. Therefore, the mechanism of the occurrence of intraatomic diamagnetic current in the neutral He atoms suggested in this research would not be true for materials with large sizes. The dependence of electronic properties on temperature in the diamagnetic currents in the neutral He atoms with microscopic sizes is studied and compared with that in the conventional superconductivity with macroscopic sizes.