<p>PROBLEM TO BE SOLVED: To provide an optical module that allows package connection excellent in high-frequency electrical characteristics.SOLUTION: An optical module includes: an enclosure 1_1; a high-frequency electrode 1_2 applying electric field to an optical semiconductor device in the enclosure 1_1; and a flexible substrate 2_1 electrically connected to the optical semiconductor device via a high-frequency line end 2_2. The density of a metallic material of a region 2_3 on a rear surface of the flexible substrate 2_1 on which the high-frequency line end 2_2 is provided is set to be smaller than the density of a metallic material of a ground surface 2_5 so that the high-frequency electrode 2_1 and the high-frequency line end 2_2 are previously impedance matched.</p>
