A linear power supply comprising: a P-channel or PNP first output transistor connected between an input terminal of an input voltage (Vin) and an output terminal of an output voltage (Vout); an N-channel or NPN second output transistor connected in parallel to the first output transistor; and a control circuit arranged to switch between a first mode and a second mode in accordance with the input voltage, the first mode using the first output transistor while the second mode using the second output transistor as the output transistor to generate the output voltage from the input voltage, characterized in that the control circuit includes: a first control unit arranged to generate a first control voltage according to the input voltage so as to supply the first control voltage to the first output transistor, and a second control unit arranged to generate a predetermined second control voltage so as to supply the second control voltage to the second output transistor, wherein the first control unit turns on/off the first output transistor in accordance with a result of comparison between the input voltage and a predetermined threshold value voltage, wherein the first control unit includes: an upper side current source (P2, P3 and N1) connected between the input terminal of the input voltage and a control terminal of the first output transistor so as to generate an upper side current, a lower side current source connected between the control terminal of the first output transistor and a ground terminal so as to generate a lower side current, and an input voltage monitoring unit (P1, DS1 and ZD1) arranged to turn on/off the upper side current source in accordance the result of comparison between the input voltage and the threshold value voltage, wherein the input voltage monitoring unit includes: a current source having a first terminal connected to an application terminal of the input voltage, a diode or a diode array having an anode connected to a second terminal of the current source and a cathode connected to a control terminal of the upper side current source, and a zener diode having a cathode connected to the control terminal of the upper side current source and an anode connected to the ground terminal. a P-channel or PNP first output transistor connected between an input terminal of an input voltage (Vin) and an output terminal of an output voltage (Vout); an N-channel or NPN second output transistor connected in parallel to the first output transistor; and a control circuit arranged to switch between a first mode and a second mode in accordance with the input voltage, the first mode using the first output transistor while the second mode using the second output transistor as the output transistor to generate the output voltage from the input voltage, characterized in that a first control unit arranged to generate a first control voltage according to the input voltage so as to supply the first control voltage to the first output transistor, and a second control unit arranged to generate a predetermined second control voltage so as to supply the second control voltage to the second output transistor, wherein an upper side current source (P2, P3 and N1) connected between the input terminal of the input voltage and a control terminal of the first output transistor so as to generate an upper side current, a lower side current source connected between the control terminal of the first output transistor and a ground terminal so as to generate a lower side current, and an input voltage monitoring unit (P1, DS1 and ZD1) arranged to turn on/off the upper side current source in accordance the result of comparison between the input voltage and the threshold value voltage, wherein a current source having a first terminal connected to an application terminal of the input voltage, a diode or a diode array having an anode connected to a second terminal of the current source and a cathode connected to a control terminal of the upper side current source, and a zener diode having a cathode connected to the control terminal of the upper side current source and an anode connected to the ground terminal.