To provide a torque estimating device for a compressor capable of accurately estimating torque at startup of a compressor.

The torque estimating device for the compressor can be utilized for a system provided with a refrigeration cycle in which a coolant is circulated by the compressor driven by a driving source mounted on a vehicle, and has a startup determination means determining the actual start of the compressor; and a torque estimating means for estimating torque of the compressor based on a passing time from after the determination of the start of compressor by the startup determination means. The startup determination means determines startup of the compressor based on pressure variation of the refrigeration cycle and the torque estimating means further estimates the torque of the compressor while considering a amount of coolant circulation calculated based on the passing time.