A downhole tool member for hydrocarbon resource recovery, comprising a shaped body of a polyglycolic acid resin blended with an inorganic or organic short fiber reinforcement material, and having thickness reduction rate characteristics when held in water at 120° C., inclusive of: an initial thickness reduction rate (as an average for a holding period for 4 hours) which is at most 0.8 times that of a shaped body of the polyglycolic acid resin alone, and has a terminal thickness reduction rate (after the thickness decreases to 50% or less of an initial thickness) which is larger than 1.5 times the initial thickness reduction rate.