a member which is a sliding part of a gas turbine and which is subjected to a temperature of about 400° C. to about 800° C., said member which is a sliding part being plastic worked at high temperature or room temperature by forging, rolling or pressing from a cobalt-based alloy which comprises 15-35 wt % of chromium, 0.02-1.5 wt % of silicon, 0.5-4.0 wt % of nickel and 0.01-0.2 wt % of carbon, at least one species selected from five refractory metals including 1-12 wt % of molybdenum, 0.3-8 wt % of niobium, 1-20 wt % of tungsten, 1-10 wt % of tantalum, 1-10 wt % of rhenium, 0.43-4 wt % of manganese, 0.5-4 wt % of iron, and said nickel, manganese, and iron such that their total amount is in the range of 1.43-9 wt %, with the remainder being cobalt and inevitable impurities, with the total amount of said five refractory metals not less than 8.59 wt % and not exceeding 10% (by atomic ratio) of the entirety of the alloy excluding carbon

wherein said member which is a sliding part is one of a seal pin, which is provided on the shank of a turbine blade to protect the turbine blade from vibration and to seal the cooling air; and a sealing plate, which is provided on a transition piece which introduces high-temperature gas from the combustor liner to the turbine to seal said high-temperature gas.