TSUBAME is a university-built small satellite mission to measure polarization of hard X-ray photons (30-100 keV) from gamma-ray bursts using azimuthal angle anisotropy of Compton-scattered photons. Polarimetry in the hard X-ray and soft gamma-ray band should play a crucial role in the understanding of high energy emission mechanisms and the distribution of magnetic fields and radiation fields. TSUBAME has two instruments: the Wide-field Bust Monitor (WBM) and the Hard X-ray Compton Polarimeter (HXCP). The WBM detects a burst and determines on board the direction of the burst occurrence with an accuracy of 10 degrees. The spacecraft is then slewed to the GRB in 15 seconds from the trigger using CMG, a high speed attitude control device. HXCP will measure the polarized X-ray photons from the GRB while the spacecraft is slowly spinning around the bore sight. In this paper, we present an overview of the TSUBAME mission, its expected performance of X-ray polarization measurement based on Monte Carlo simulation, and the detectors.