off the operation of boost dc dc converter 103 step st 307 and the process proceeds to step st 303 accordingly vehicle mounted power source apparatus 100 starts charging low voltage battery 107 in contrast when determining that the voltage value vl is greater than the second threshold value step st 306 no control section 109 determines whether the voltage value vh of high voltage battery 105 is the third threshold value or less step st 308 when determining that the voltage value vh is the third threshold value or less step st 308 yes the process returns to step st 305 accordingly vehicle mounted power source apparatus 100 continuously charges high voltage battery 105 in contrast when determining that the voltage value vh is greater than the third threshold value step st 308 no control section 109 turns off the operation of boost dc dc converter 103 step st 309 and ends the charging process in the embodiment when both of low voltage battery 107 and high voltage battery 105 are charged with electrical power obtained by solar power generation switching is performed so that high voltage battery 105 is charged after low voltage battery 107 that requires no boosting good charge efficiency is charged as a result it is possible to prevent a decrease in the overall charge efficiency of the apparatus in.