Abstract: A measurement device has a sensor and includes a cylindrical housing, an optical fiber that is disposed along the long-side direction of the housing and that has one end disposed in the housing and the other end disposed outside the housing, a first substrate including a light receiving unit disposed on an extension of the one end in the housing, and a second substrate that is electrically connected to the first substrate via a flexible part having flexibility and is disposed at an acute angle or a right angle with respect to the first substrate.