A bicycle crank transmission apparatus includes: a hollow shaft member; a base plate coupled to the shaft member on one side and installed securely on a bottom bracket featuring a spindle on the other side; a chainring housing coupled to the shaft member in a way that allows its rotation and having a ring gear installed securely inside; a reduction gear unit arranged in the middle of the ring gear; a directly-coupled ratchet unit installed on the ring gear; a crank cover where a coupling shaft coupled to the spindle is perpendicularly provided in the center and where clutch ratchet teeth, which are engaged with the directly-coupled ratchet unit, and directly-coupled ratchet teeth are vertically stacked on the internal wall surface; and a sun gear installed on the coupling shaft in such a way that it only rotates in clockwise direction and partially engaged with the reduction gear unit.