A downhole tool member for hydrocarbon resource recovery, comprising a shaped body of a polyglycolic acid resin having a weight average molecular weight of at least 70,000, having an effective thickness which is ½ or more of a critical thickness of surface decomposition, and exhibiting a thickness reduction rate in water which is constant with respect to time. As a result, it has become possible to more accurately design the strength and time up to the collapse of the downhole tool member which forms the whole or a part of a downhole tool for developing or repairing downholes for recovery of hydrocarbon resources, such as oil and gas.