In recent years, a wide band communication system in which a UWB is applied and a radio LAN have been applied in diverse fields.  For example, mobile terminals such as a personal computer (hereinafter, referred to as “PC”) having a communication function owing to the UWB or the radio LAN, a cellular phone, and a personal digital assistance (PDA) have arrived. 
Because various band frequencies are used in the UWB, the UWB antenna having a band as wide as possible is desired.  In particular, an antenna to be incorporated into the mobile terminal is desirably high in performance and wide in band while being small in size and low in costs. 
The conventional mobile terminal antenna had problems inherent therein such as its installation portion and a size of a ground conductor, that is, a ground portion.  There are various kinds of mobile terminals such as a PC, a cellular phone, and a PDA.  The configuration of a package differs according to a maker or a model even if the category is identical.  The design or the like is usually changed every time a new function is added thereto even if the model is identical.  Since the conventional wide band antenna (broad band antenna) is configured by the ground portion and an emission element portion in cooperation, there arise such problems that it is impossible to realize the wide band property, the antenna performance is remarkably changed with a change in installation portion of the antenna or a difference in the size of the ground portion. 
An object of the present invention is to provide a wide band antenna capable of maintaining the wide band property without being affected by the change in the installation portion of the antenna or the size of the ground portion.