A power amplifying device comprising: a distribution line which is adapted to distribute power; a plurality of power amplifying elements which is provided at a stage subsequent to the distribution line and is adapted to amplify the power distributed from the distribution line; a connection line which is provided at a stage subsequent to each of the power amplifying elements and is adapted to combine the outputs of the power amplifying elements; an output line which is connected to the connection line; a filter (11, 11') comprising a filter element, the filter being connected to the connection line or to the output line, and being adapted to filter a predetermined frequency included in a high frequency signal transmitted to the connection line or the output line; a first directional coupler which is provided at a stage subsequent to the filter (11, 11'), and which is adapted to output the high frequency signal transmitted to the output line, to a RF monitor terminal; Characterized in that the amplifying device comprises: a second directional coupler which is provided at a stage subsequent to the filter (11, 11'), and which is adapted to output the high frequency signal transmitted to the output line, to a level detection detector; and in that said filter is provided in a package in which said connection line is also provided; and wherein the filter element has a filter body wherein said filter consists of the filter body of the filter element; and wherein the amplifying device is adapted to reduce leakage of a harmonic produced by the level detection detector to the RF monitor output terminal by adjusting the degrees of coupling of the first and second directional couplers. a distribution line which is adapted to distribute power; a plurality of power amplifying elements which is provided at a stage subsequent to the distribution line and is adapted to amplify the power distributed from the distribution line; a connection line which is provided at a stage subsequent to each of the power amplifying elements and is adapted to combine the outputs of the power amplifying elements; an output line which is connected to the connection line; a filter (11, 11') comprising a filter element, the filter being connected to the connection line or to the output line, and being adapted to filter a predetermined frequency included in a high frequency signal transmitted to the connection line or the output line; a first directional coupler which is provided at a stage subsequent to the filter (11, 11'), and which is adapted to output the high frequency signal transmitted to the output line, to a RF monitor terminal; Characterized in that the amplifying device comprises: a second directional coupler which is provided at a stage subsequent to the filter (11, 11'), and which is adapted to output the high frequency signal transmitted to the output line, to a level detection detector; and in that said filter is provided in a package in which said connection line is also provided; and wherein the filter element has a filter body wherein said filter consists of the filter body of the filter element; and wherein the amplifying device is adapted to reduce leakage of a harmonic produced by the level detection detector to the RF monitor output terminal by adjusting the degrees of coupling of the first and second directional couplers.