Alight-detecting device (1A, 1B, 1C, 1D) comprising: a Fabry-Perot interference filter having a first mirror and a second mirror and being provided with an opening to pass light transmitted according to a distance between the first mirror and the second mirror along a predetermined direction, the distance between the first mirror and the second mirror being variable, the Fabry-Perot interference filter further having a sacrificial layer of a frame shape forming a gap between the first mirror and the second mirror; a light detector having a light reception unit to receive the light having passed through the opening, the light reception unit and the opening facing each other; a wiring substrate, the light detector being mounted on the wiring substrate; and a support member (4, 64) supporting the Fabry-Perot interference filter on the wiring substrate, such that a second space is formed between the Fabry-Perot interference filter and the wiring substrate, the second space being continuous with a first space in the opening and including the first space when viewed from the predetermined direction, wherein the light detector is disposed in the second space, and the light reception unit is disposed in a region corresponding to the first space in the second space, when viewed from the predetermined direction, characterized in that: a depth of the opening in the predetermined direction is greater than the thickness of the sacrificial layer, such that optical interference between the Fabry-Perot interference filter and the light detector becomes hard to occur. a Fabry-Perot interference filter having a first mirror and a second mirror and being provided with an opening to pass light transmitted according to a distance between the first mirror and the second mirror along a predetermined direction, the distance between the first mirror and the second mirror being variable, the Fabry-Perot interference filter further having a sacrificial layer of a frame shape forming a gap between the first mirror and the second mirror; a light detector having a light reception unit to receive the light having passed through the opening, the light reception unit and the opening facing each other; a wiring substrate, the light detector being mounted on the wiring substrate; and a support member (4, 64) supporting the Fabry-Perot interference filter on the wiring substrate, such that a second space is formed between the Fabry-Perot interference filter and the wiring substrate, the second space being continuous with a first space in the opening and including the first space when viewed from the predetermined direction, wherein the light detector is disposed in the second space, and the light reception unit is disposed in a region corresponding to the first space in the second space, when viewed from the predetermined direction, characterized in that: a depth of the opening in the predetermined direction is greater than the thickness of the sacrificial layer, such that optical interference between the Fabry-Perot interference filter and the light detector becomes hard to occur. a depth of the opening in the predetermined direction is greater than the thickness of the sacrificial layer, such that optical interference between the Fabry-Perot interference filter and the light detector becomes hard to occur.