An electronic-component mount substrate includes a substrate having a first principal surface and a second principal surface opposite to the first principal surface; a mount electrode for mounting an electronic component on the first principal surface, the mount electrode having a first slit and sandwiching the first slit; a plane electrode surrounding the mount electrode in a plan view and having a second slit; a connection electrode connecting the mount electrode with the plane electrode; and an outer electrode on the second principal surface. The connection electrode overlaps the outer electrode and an outer edge of the outer electrode surrounds the connection electrode in a perspective plan view.