A power transmission device in which a driven body and a driving body for driving the driven body are rotated in the same direction and are connected together by a connection section to transmit torque of the driving body to the driving body and in which the transmission of the torque from the driving body is interrupted when a drive load on the driven body exceeds a predetermined level. The connection section is constructed by combining separate elements that are a positive torque transmission member, and a negative torque transmission mechanism or a negative torque transmission member. The positive torque transmission member transmits torque in the normal rotation direction and interrupts transmission of torque from the driving body by breaking itself when a drive load on the driven body exceeds the predetermined level. The negative torque transmission mechanism or the negative torque transmission member can transmit torque in the reverse rotation direction. In the power transmission device, fatigue of materials of the connection section is suppressed and torque is accurately interrupted at a desired interruption torque value.