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).