An RFID tag comprising: a base part made of dielectric material and having plate-like shape; a loop antenna (140, 240) formed around the base part, the loop antenna including a first antenna element and a second antenna element, the loop antenna having a loop-length shorter than a wavelength of a resonant frequency; and an IC chip placed at a first surface side of the base part, the IC chip being connected between a first terminal disposed on a first end of the first antenna element and a second terminal disposed on a first end of the second antenna element, wherein the loop antenna (140, 240) includes an overlapping part placed at a second surface side of the base part, a first end part disposed on a second end of the first antenna element and a second end part disposed on a second end of the second antenna element being overlapped at the overlapping part, the first end part and the second end part being insulated from each other, wherein a capacitance of the overlapping part is configured to be adjusted such that a difference between an imaginary component of a first synthetic impedance and an imaginary component of a second synthetic impedance is less than or equal to a predetermined value, the imaginary component of the first synthetic impedance viewed from the first terminal and the second terminal being obtained based on an inductance of the loop antenna (140, 240) in a case where the second surface side of the base part is attached to a metallic member, a capacitance obtained between the loop antenna (140, 240) and the metallic member and the capacitance of the overlapping part, the imaginary component of the second synthetic impedance viewed from the first terminal and the second terminal being obtained based on an inductance of the loop antenna (140, 240) in a case where the second surface side of the base part is attached to a non-metallic member and the capacitance of the overlapping part. a base part made of dielectric material and having plate-like shape; a loop antenna (140, 240) formed around the base part, the loop antenna including a first antenna element and a second antenna element, the loop antenna having a loop-length shorter than a wavelength of a resonant frequency; and an IC chip placed at a first surface side of the base part, the IC chip being connected between a first terminal disposed on a first end of the first antenna element and a second terminal disposed on a first end of the second antenna element, wherein the loop antenna (140, 240) includes an overlapping part placed at a second surface side of the base part, a first end part disposed on a second end of the first antenna element and a second end part disposed on a second end of the second antenna element being overlapped at the overlapping part, the first end part and the second end part being insulated from each other, wherein a capacitance of the overlapping part is configured to be adjusted such that a difference between an imaginary component of a first synthetic impedance and an imaginary component of a second synthetic impedance is less than or equal to a predetermined value, the imaginary component of the first synthetic impedance viewed from the first terminal and the second terminal being obtained based on an inductance of the loop antenna (140, 240) in a case where the second surface side of the base part is attached to a metallic member, a capacitance obtained between the loop antenna (140, 240) and the metallic member and the capacitance of the overlapping part, the imaginary component of the second synthetic impedance viewed from the first terminal and the second terminal being obtained based on an inductance of the loop antenna (140, 240) in a case where the second surface side of the base part is attached to a non-metallic member and the capacitance of the overlapping part.