In this study, a Pd–Si–Cu metallic glass was applied to a torsional resonator with long torsion beams. It is challenging to obtain the excellent mechanical performances of metallic glass when applied to torsional resonators with a low spring constant. The resonant frequency is evaluated using a laser Doppler vibrometer, and a fundamental resonant frequency of 1438 Hz and a torsional resonant frequency of 1908 Hz are obtained. When the resonant frequency is compared to the simulation results using the finite element method, a tensile stress of 25 MPa is expected for the beam part combining the residual stress and deformation. The rotational spring constant is 8.8 × 104 pNm/rad, and the displacement of the stage per unit torque is estimated to be 5.7 pm/fNm. We propose a torsional resonator with metallic glass without residual stress and initial deformation for the detection of small torques such as quantum spins.