An antenna driving apparatus comprising: a direct current power source configured to supply direct current power to a human detecting IC of a vehicle-mounted apparatus configured to detect contact to a human detecting area of a vehicle by a user of the vehicle, the direct current power source outputting a direct current power source voltage (V DC ) to a first connecting line electrically connected to a power source terminal of the human detecting IC and outputting a reference potential (V GND ) to a second connecting line electrically connected to a GND terminal of the human detecting IC; an antenna driving circuit configured to drive an antenna that transmits a signal to a portable device carried by the user, the antenna driving circuit being configured to output a first antenna drive signal (V AC1 ) generated by switching between the direct current power source voltage (V DC ) and the reference potential (V GND ) to the first connecting line electrically connected to one end of the antenna and outputting a potential difference between the first antenna drive signal (V AC1 ) and a second antenna drive signal (V AC2 ) to be output to the second connecting line electrically connected to the other end of the antenna to the antenna as an antenna drive signal; and a control unit configured to perform switching control of the direct current power source voltage (V DC ) and the antenna drive signal to be output to the first connecting line and the second connecting line and to perform switching control of the antenna driving circuit , and. a step-up/step-down circuit configured to step up and step down the direct current power source voltage (V DC ) and output a stepped-up and stepped-down voltage, wherein the antenna driving circuit generates the second antenna drive signal (V AC2 ) to be output to the second connecting line by switching the stepped-up and stepped-down voltage and the reference potential (V GND ). a direct current power source configured to supply direct current power to a human detecting IC of a vehicle-mounted apparatus configured to detect contact to a human detecting area of a vehicle by a user of the vehicle, the direct current power source outputting a direct current power source voltage (V DC ) to a first connecting line electrically connected to a power source terminal of the human detecting IC and outputting a reference potential (V GND ) to a second connecting line electrically connected to a GND terminal of the human detecting IC; an antenna driving circuit configured to drive an antenna that transmits a signal to a portable device carried by the user, the antenna driving circuit being configured to output a first antenna drive signal (V AC1 ) generated by switching between the direct current power source voltage (V DC ) and the reference potential (V GND ) to the first connecting line electrically connected to one end of the antenna and outputting a potential difference between the first antenna drive signal (V AC1 ) and a second antenna drive signal (V AC2 ) to be output to the second connecting line electrically connected to the other end of the antenna to the antenna as an antenna drive signal; and a control unit configured to perform switching control of the direct current power source voltage (V DC ) and the antenna drive signal to be output to the first connecting line and the second connecting line and to perform switching control of the antenna driving circuit , and. a step-up/step-down circuit configured to step up and step down the direct current power source voltage (V DC ) and output a stepped-up and stepped-down voltage, wherein the antenna driving circuit generates the second antenna drive signal (V AC2 ) to be output to the second connecting line by switching the stepped-up and stepped-down voltage and the reference potential (V GND ). <EOS>