A multi-band monopole antenna includes a first radiation conductor portion formed with a rod member having a length defined in accordance with a wavelength of a first frequency included in a predetermined first frequency band among plural frequency bands, and a second radiation conductor portion integrally connected with the first radiation conductor portion and formed with a planar member in which a direct distance from a feeding portion to a farthest point which is the farthest position from the feeding portion is defined in accordance with a wavelength of a second frequency included in a second frequency band which differs from the first frequency band among the plural frequency bands. The feeding portion is provided at a position based on the length defined in accordance with the wavelength of the first frequency relative to a position of a tip end of the first radiation conductor portion.