New core (Liqualloy^TM core) made of soft magnetic Fe-based glassy alloy powder was fabricated by the consolidation using an uni-axial mechanical press at room temperature. This new core has the constant relative permeability (μ') of about 60 up to 1 MHz and extremely low core loss blow 200kW/m³ at f=100kHz and B_m=0.1 T. The efficiency of the switching power supply (η) was improved by 2∼3% when the Liqualloy^TM core was used instead of Fe-Al-Si core. The temperature rise near the Liqualloy^TM core (ΔT) was also 10K lower than that of the Fe-Al-Si core. These excellent properties of the Liqualloy^TM core are based on its extremely low hysteresis and eddy current losses. These low losses are originated from its good soft magnetic properties (Hc=2A/m) after annealing at relatively low temperature, its intrinsic hardness (Hv=1000) and high resistivitiy (ρ=160μΩcm).