An engine start device being characterized by comprising: a rotation drive section; a rotation driven section to which a rotation of the rotation drive section is transmitted; and damping and accumulating means (9, 10) interposed between the rotation drive section and the rotation driven section, the damping and accumulating means (9, 10) accumulating a force while damping on the basis of a driving of the rotation drive section in a process of the driving the rotation drive section, and starting up an engine via the rotation driven section on the basis of the accumulated force, wherein the damping and accumulating means (9, 10) has mode switching means for switching a mode from a first start mode in which the rotation of the rotation drive section is directly transmitted to the rotation driven section via the damping and accumulating means (9, 10), to a second start mode in which the rotation of the rotation drive section exclusively accumulates the force in the damping and accumulating means (9, 10) and releases the accumulated force accumulated in the damping and accumulating means (9, 10) at a desired time so as to rotate the rotation driven section, and the mode switching means has first and second engaging and disengaging members (14, 15) which engage with and disengage from each of the damping and accumulating means (9, 10) and the rotation driven section so as to respectively inhibit and allow a reverse rotation of the damping and accumulating means (9, 10) and the rotation driven section, and user operable single switch operating means which engages with and disengages from the damping and accumulating means (9, 10) and the rotation driven section in cooperation with the first and second engaging and disengaging members (14, 15), whereby the accumulated force accumulated in the damping and accumulating means (9, 10) is released at a desired time by operating the single switch operating means so as to rotate the rotation driven section wherein the first and second engaging and disengaging members (14, 15) are engaged with and disengaged from the damping and accumulating means (9, 10) and the rotation driven section at a switching time of the second start mode on the basis of an operation of the switch operating means in such a manner that an engagement of the first engaging and disengaging member is disengaged after a desired time has elapsed after disengaging an engagement of the second engaging and disengaging member by a time difference mechanism. a rotation drive section; a rotation driven section to which a rotation of the rotation drive section is transmitted; and damping and accumulating means (9, 10) interposed between the rotation drive section and the rotation driven section, the damping and accumulating means (9, 10) accumulating a force while damping on the basis of a driving of the rotation drive section in a process of the driving the rotation drive section, and starting up an engine via the rotation driven section on the basis of the accumulated force, wherein the damping and accumulating means (9, 10) has mode switching means for switching a mode from a first start mode in which the rotation of the rotation drive section is directly transmitted to the rotation driven section via the damping and accumulating means (9, 10), to a second start mode in which the rotation of the rotation drive section exclusively accumulates the force in the damping and accumulating means (9, 10) and releases the accumulated force accumulated in the damping and accumulating means (9, 10) at a desired time so as to rotate the rotation driven section, and the mode switching means has first and second engaging and disengaging members (14, 15) which engage with and disengage from each of the damping and accumulating means (9, 10) and the rotation driven section so as to respectively inhibit and allow a reverse rotation of the damping and accumulating means (9, 10) and the rotation driven section, and user operable single switch operating means which engages with and disengages from the damping and accumulating means (9, 10) and the rotation driven section in cooperation with the first and second engaging and disengaging members (14, 15), whereby the accumulated force accumulated in the damping and accumulating means (9, 10) is released at a desired time by operating the single switch operating means so as to rotate the rotation driven section wherein the first and second engaging and disengaging members (14, 15) are engaged with and disengaged from the damping and accumulating means (9, 10) and the rotation driven section at a switching time of the second start mode on the basis of an operation of the switch operating means in such a manner that an engagement of the first engaging and disengaging member is disengaged after a desired time has elapsed after disengaging an engagement of the second engaging and disengaging member by a time difference mechanism.