A molecular fluorine laser system includes a discharge chamber filled with a gas mixture at least including molecular fluorine and a buffer gas, multiple electrodes within the discharge chamber and connected to a discharge circuit for energizing the gas mixture, and a resonator for generating an output beam. The segmented ball seat valve provides communication between the inside of the pipe and the well bore or casing through open ports. Each of the channels is defined by an opening opened toward a direction parallel to the rotational axis and a surface portion formed by extending the opening to a direction along the rotational axis. The plurality of drive force transmission gears, provided for each of the image carriers, transmits a driving force from the drive unit to the image carriers.