The present invention solves the above-described problems, and is a torque transmission device including: a low-torque input means 8; output rotating means 11 configured to be magnetically coupled with the low-torque input means so as to generate a thrust force in response to a load; and high-torque input means 15 configured to engage the output rotating means 11 at the time of a high-load rotation and transmits a torque, wherein the low-torque input means 8 includes: pole teeth 9 configured to oppose the magnetic pole rotating bodies 12 of the output rotating means to be magnetically coupled thereto at the time of low-load rotation, and side magnetic bodies 10 configured to oppose the magnetic pole rotating bodies 12 slid by a thrust force generated by the relative rotation between the magnetic pole rotating bodies 12 and the pole teeth 9 and to be magnetically coupled thereto at the time of high-load rotation, the output rotating means includes the magnetic pole rotating bodies 12, a permanent magnet 13 clamped between the magnetic pole rotating bodies 12, and a claw clutch portion 14 configured to engage the high-torque input means 15 at the time of high-load rotation. The torque transmission device of the related art has a problem in that the power transmission cannot necessarily be achieved sufficiently at the time of the high-load and clutch performance may not function sufficiently. Also, a rotation-thrust converting mechanism for causing the speed switching member to operate includes, a converting mechanism having an intermediate disk provided with a permanent magnet and an output disk provided with a magnetism for a magnetic spring which provides a returning force to a magnet for moving the intermediate disk, and the intermediate disk, and the converting mechanism being complicated in configuration and having a large number of components is provided separately from the transmission body, so that the configuration of the transmission becomes complicated and large-sized and, since the number of the components is increased, the cost is also increased.