Measuring device, in the form of a laser scanner, for optically measuring an environment, comprising a measuring head, the housing of which is mounted rotatably about a base axis on a base, and comprising - a beam source integrated in the housing of the measuring head and serving for generating a transmission light beam, - a reception sensor integrated in the housing of the measuring head and serving for detecting a reflected transmission light beam returning as a reception light beam, and - comprising a rotation unit, which is mounted on a side of the housing which is opposite the beam source, the reception sensor and optical components and which has a rotation body, which is mounted rotatably about its rotation axis at least on one side, with a deflection element for the aligned deflection of the transmission light beam into the environment and for the capture and deflection of the reception light beam, wherein - the rotation body is substantially cylindrical and the rotation axis is its cylinder axis; and wherein - a direction of incidence in which the transmission light beam impinges on the deflection element during operation corresponds to the alignment of the rotation axis, and - wherein basis axis and rotation axis are substantially perpendicular to one another, - a targeting element is integrated in the rotation body, - the rotation body has an opening passing through the rotation body, which opening is part of the targeting element and through which opening it is possible for viewing to be carried out and a target can be aimed at, characterized in that - a viewing direction through the targeting element or through the through opening of the targeting element and the direction of incidence of the transmission light beam on the deflection element and a deflecting direction in which the transmission light beam is deflected by the deflection element are in each case perpendicular to one another. - a beam source integrated in the housing of the measuring head and serving for generating a transmission light beam, - a reception sensor integrated in the housing of the measuring head and serving for detecting a reflected transmission light beam returning as a reception light beam, and - comprising a rotation unit, which is mounted on a side of the housing which is opposite the beam source, the reception sensor and optical components and which has a rotation body, which is mounted rotatably about its rotation axis at least on one side, with a deflection element for the aligned deflection of the transmission light beam into the environment and for the capture and deflection of the reception light beam, wherein - the rotation body is substantially cylindrical and the rotation axis is its cylinder axis; and wherein - a direction of incidence in which the transmission light beam impinges on the deflection element during operation corresponds to the alignment of the rotation axis, and - wherein basis axis and rotation axis are substantially perpendicular to one another, - a targeting element is integrated in the rotation body, - the rotation body has an opening passing through the rotation body, which opening is part of the targeting element and through which opening it is possible for viewing to be carried out and a target can be aimed at, - a viewing direction through the targeting element or through the through opening of the targeting element and the direction of incidence of the transmission light beam on the deflection element and a deflecting direction in which the transmission light beam is deflected by the deflection element are in each case perpendicular to one another.