The invention relates to an internal dual band antenna meant for small radio devices, an antenna module and a radio device, which has an antenna implemented with the antenna module. The antenna contains two radiators (7, 8) and a parasite element (14), which is shared between them. The parasite element (14) is mainly implemented on three sides of the antenna module, which sides are perpendicular to the side, where two radiators are implemented. The short-circuit conductor (12) of the parasite element (14) extends close to the supply point/points (3, 4) of the antenna in the direction of the level of the circuit board of the radio device, from which location (5) it is connected to the ground plane (11) of the radio device. The antenna structure is dimensioned so that the two resonance frequencies based on the parasite element (14) are on both functional bands at a lower frequency than the resonance frequencies of the actual radiators (7, 8). By proceeding thus, both the lower and upper frequency band is widened. The shape of the parasite element is such that the hand of a user of the radio device does not essentially weaken the adaptation of the antenna in either functional band.