A charging apparatus comprising: two charging terminals (6a, 6b) configured to be connected to a storage battery; a large-current charging circuit configured to generate a first charging current; a small-current charging circuit configured to generate a second charging current that is smaller than the first charging current; a switching element selectively connecting the large-current charging circuit to one of the two charging terminals (6a, 6b); and a power terminal (5a, 5b); wherein the large-current charging circuit and the small-current charging circuit are connected in cascade between the power terminal (5a, 5b) and the charging terminal (6a, 6b); characterized in that the switching element is a p-channel field-effect transistor and is connected to the small-current charging circuit in parallel; the small-current charging circuit is adapted to variably control the second charging current in a linear manner or in a plurality of steps in accordance with the voltage of the storage battery; and the charging apparatus further comprises a line switching controller adapted to detect a voltage of the storage battery, wherein the line switching controller includes including an NPN-type transistor and a microcontroller; wherein a resistor is connected between a gate and a source of the p-channel field-effect transistor; an emitter of the NPN-type transistor is connected to the other of the two charging terminals (6a, 6b); a collector of the NPN-type transistor is connected to the gate of the p-channel field-effect transistor; and the microcontroller is connected to the two charging terminals (6a, 6b) and is adapted to activate the NPN-type transistor to activate the p-channel field-effect transistor when a detected voltage is smaller than a predetermined value, and to deactivate the NPN-type transistor to deactivate the p-channel field-effect transistor when the detected voltage is larger than or equal to the predetermined value. two charging terminals (6a, 6b) configured to be connected to a storage battery; a large-current charging circuit configured to generate a first charging current; a small-current charging circuit configured to generate a second charging current that is smaller than the first charging current; a switching element selectively connecting the large-current charging circuit to one of the two charging terminals (6a, 6b); and a power terminal (5a, 5b); wherein the large-current charging circuit and the small-current charging circuit are connected in cascade between the power terminal (5a, 5b) and the charging terminal (6a, 6b); characterized in that the switching element is a p-channel field-effect transistor and is connected to the small-current charging circuit in parallel; the small-current charging circuit is adapted to variably control the second charging current in a linear manner or in a plurality of steps in accordance with the voltage of the storage battery; and the charging apparatus further comprises a line switching controller adapted to detect a voltage of the storage battery, wherein the line switching controller includes including an NPN-type transistor and a microcontroller; wherein a resistor is connected between a gate and a source of the p-channel field-effect transistor; an emitter of the NPN-type transistor is connected to the other of the two charging terminals (6a, 6b); a collector of the NPN-type transistor is connected to the gate of the p-channel field-effect transistor; and the microcontroller is connected to the two charging terminals (6a, 6b) and is adapted to activate the NPN-type transistor to activate the p-channel field-effect transistor when a detected voltage is smaller than a predetermined value, and to deactivate the NPN-type transistor to deactivate the p-channel field-effect transistor when the detected voltage is larger than or equal to the predetermined value.