An optical antenna device (1; 1A) comprising: an optical lens system configured to focus a laser beam incident thereon; an optical-system holding member including a flange portion configured to hold an outer peripheral edge of the optical lens system, and an engagement portion formed between an outer circumferential surface of the optical lens system and an inner circumferential surface of the flange portion; an optical connection member placed on a rear focal plane of the optical lens system; a first shaft portion (15A to 15D; 35A to 35D) extending along an optical axis direction of the optical lens system from a rear end portion of the flange portion toward the optical connection member, and having a first linear expansion coefficient in the optical axis direction; and a second shaft portion (16A to 16D; 36A to 36D) extending along the optical axis direction from a front surface of the optical connection member toward the flange portion of the optical-system holding member, and having a second linear expansion coefficient different from the first linear expansion coefficient in the optical axis direction, characterized in that: the first shaft portion (15A to 15D; 35A to 35D) and the second shaft portion (16A to 16D; 36A to 36D) are fixedly connected to each other at a predetermined fixing position between the rear end portion of the flange portion and the front surface of the optical connection member, and an effective linear expansion coefficient of the first and second shaft portions (15A to 15D, 16A to 16D; 35A to 35D, 36A to 36D) as a whole is expressed by a linear combination expression given by γ = c × α + 1 − c × β, where c denotes a ratio of a length of the first shaft portion (15A to 15D; 35A to 35D) from the rear end portion of the flange portion to the fixing position, to a flange back between the optical-system holding member and the optical connection member, 1 - c denotes a ratio of a length of the second shaft portion (16A to 16D; 36A to 36D) from the front surface of the optical connection member to the fixing position, to the flange back, α denotes the first linear expansion coefficient, β denotes the second linear expansion coefficient, and γ denotes the effective linear expansion coefficient. an optical lens system configured to focus a laser beam incident thereon; an optical-system holding member including a flange portion configured to hold an outer peripheral edge of the optical lens system, and an engagement portion formed between an outer circumferential surface of the optical lens system and an inner circumferential surface of the flange portion; an optical connection member placed on a rear focal plane of the optical lens system; a first shaft portion (15A to 15D; 35A to 35D) extending along an optical axis direction of the optical lens system from a rear end portion of the flange portion toward the optical connection member, and having a first linear expansion coefficient in the optical axis direction; and a second shaft portion (16A to 16D; 36A to 36D) extending along the optical axis direction from a front surface of the optical connection member toward the flange portion of the optical-system holding member, and having a second linear expansion coefficient different from the first linear expansion coefficient in the optical axis direction, the first shaft portion (15A to 15D; 35A to 35D) and the second shaft portion (16A to 16D; 36A to 36D) are fixedly connected to each other at a predetermined fixing position between the rear end portion of the flange portion and the front surface of the optical connection member, and an effective linear expansion coefficient of the first and second shaft portions (15A to 15D, 16A to 16D; 35A to 35D, 36A to 36D) as a whole is expressed by a linear combination expression given by γ = c × α + 1 − c × β, where c denotes a ratio of a length of the first shaft portion (15A to 15D; 35A to 35D) from the rear end portion of the flange portion to the fixing position, to a flange back between the optical-system holding member and the optical connection member, 1 - c denotes a ratio of a length of the second shaft portion (16A to 16D; 36A to 36D) from the front surface of the optical connection member to the fixing position, to the flange back, α denotes the first linear expansion coefficient, β denotes the second linear expansion coefficient, and γ denotes the effective linear expansion coefficient.