Theoretical Astronomy and Astrophysics. I focus on the following topics with numerical simulation. (1) Gas-giant Planet and its Satellite Formation It is considered that the gas giant planet such as Jupiter and Saturn in our solar system is formed after the gas accretes onto a solid core with several earth mass. However, we cannot well understand the gas accretion process and growth process of the gas giant planet. This study focuses on the formation and evolution of the gas giant planet and its circumplanetary disk using numerical simulation. In addition, the formation process of regular satellites around the gas giant planet is investigated. (2) Planet Formation by Gravitational Instability Recently, direct imaging of exo-planet showed that several planets orbit in the region much far from the central star. It is difficult to form such planets by classical planet formation scenario (core accretion scenario). In this study, I investigate the planet formation by gravitational instability of the disk. In this scenario, fragmentation occurs in the protoplantary disk by gravitational instability and protoplanet appears. To discuss validity of this scenario, I calculate the formation and evolution of star, disk and planet from prestellar cloud stage with nested grid simulation code. (3) Protostellar Jet and Star Formation Efficiency The star at its formation ejects a large fraction of the mass in the parent cloud by protostellar outflow. The protostellar outflow transfers an excess angular momentum of the molecular cloud. In this study, I calculate the formation of the star and propagation of protostellar outflow to determine the star formation efficiency. In addition, we compare the results by ALMA with simulations. (4) First Star Formation and Effect of the Magnetic Field It is considered that only a massive star forms in the early universe. The magnetic field is very important in the present-day star formation process because it controls the star formation efficiency and determines resulting stellar mass. In the early universe, it is expected that the magnetic field is extremely weak and hardly affects the star formation. The magnetic field largely dissipates in the collapsing gas in the present day star formation, while the magnetic field is always coupled with neutral gas in the primordial collapsing cloud. Thus, the magnetic field continues to be amplified and may affect the star formation even in the early universe. In this study, we calculate the evolution of the magnetized primordial gas cloud and investigate the effect of the magnetic field on the first star formation.