To provide an advanced device for displaying the phase of the moon in a wristwatch and other clocks.

This device includes an indicator (3) in a shape of a plate, moving behind the dial (1), that has a round aperture (2) showing a moon disk. This indicator contains an S-shaped separation line (6) between the dark space zone (4) and a light space zone (5) in the aperture, respectively, corresponding to the non-irradiated part and the irradiated part of the moon. This indicator is attached freely rotatably at a position C, based on symmetry centering of the separation line (6) on the rotation type support medium as an axis which rotates two times in approximately one lunar month. Therefore, the representation that agrees with the aspect of the moon in each moon phase is obtained. Such a device can be used especially for wristwatches and other clocks.