Abstract: The present invention decribes a high-frequency attenuator using PIN diodes, which is especially intended as power control means in a radio-telephone transmitter, and in which the input and output impedances remain constant as the attenuation is varied. The attenuator comprises a longitudinal branch between the input and the output port, having PIN diodes (D1, D2) attenuating the RF signal, transverse branches connected with the input and the output port, each comprising a quarter-wavelength transformer (C1, Z1, C2; C4, Z2, C5) viewed from the signal path and a PIN diode (D3, D4). The same control direct current passes via all the diodes. In spite of the variations of the resistance of the PIN diodes, the input and output impedances of the attenuator do not change owing to the quarter-wavelength transformer.