An electrical connecting mechanism includes: a first connector disposed at an apparatus main body; a second connector disposed at an optional device, a power feed switch disposed at one among the apparatus main body and the optional device and capable of switching between a connected state and an unconnected state; and an operation element that is disposed in the other one among the apparatus main body and the optional device, and causes a state in which power can be supplied from the apparatus main body to the optional device to be entered by changing the power feed switch to the connected state, when the first connector and the second connector are coupled.