According to an embodiment, a wireless device includes an interposer, a semiconductor chip, electrodes, and a slot antenna. The interposer includes conductive layers disposed at least at a side of a component mounting surface and a side of a reverse surface opposite to the component mounting surface. The semiconductor chip is mounted on the component mounting surface and includes a built-in transceiving circuit. The electrodes are disposed in a conductive layer disposed at the side of the reverse surface of the interposer so as to be electrically connected to an outside of the wireless device. At least a portion of the slot antenna is disposed in at least one of the conductive layers of the interposer. A shortest distance between an end in a width direction of the slot antenna and the electrodes is smaller than a sum of a minimum line width and a minimum line space of the interposer.