A hand mechanism including a first multi-joint finger, a second multi-joint finger, and a single-joint finger rotatable about a center of a predetermined connecting portion together with the first and second multi-joint fingers. The mechanism executes a first mode in which the respective entire fingers of the first and second multi-joint fingers are rotated in an identical direction using a connecting portion with respect to an attachment member when driven by a driving actuator, and a second mode in which a finger section other than a first predetermined finger section included in the first multi-joint finger is rotated with respect to the first predetermined finger section and a finger section other than a second predetermined finger section included in the second multi-joint finger is rotated with respect to the second predetermined finger section, when the rotation of the first and second predetermined finger sections are inhibited in the first mode.