A work mounting device in which an operation for teaching a robot to mount a work on a work mounting member is automated. The work is gripped by a hand placed on an arm tip portion of the robot and the operation for mounting the work on the work mounting member is taught. A plurality of distance sensors are disposed on the work mounting member or the hand. Distances between each sensor and the work or distances between each sensor and the work mounting member are measured. A robot controller maintains an attitude of the robot so that the distances detected by the distance sensors are uniform and, at the same time, allows the work to approach the work mounting member so that a plurality of holes of the work are engaged with a plurality of respective protrusions of the work mounting member. Based on the distance data detected by the distance sensors, a disturbance estimation observer, a load torque on motors for each axis or the like, the movement of the robot is stopped automatically when the work reaches a position where the work is in contact with the work mounting member or is very close to contact therewith. The position and attitude of the robot at this time is taught.