An electronic component package includes a dielectric substrate having a first surface where an electronic component is sealed. A first signal line connecting to the electronic component and a first ground conductor are formed on the first surface of the dielectric substrate. A second signal line connected to an outside connection electrode and a second ground conductor are formed on a second surface of the dielectric substrate. The first ground conductor and the second ground conductor are connected by a plurality of ground conductor via-holes. A substrate-buried signal line connected to the first signal line and the second signal line is provided inside of the dielectric substrate so as to be put between the first ground conductor and the second ground conductor above and below and between the ground conductor via-holes on the right and left.