Training bicycle and bicycle frame

A pedal unit attachable/detachable training bicycle comprising:

• a bicycle frame comprising a receiving member provided at bottom of a seat tube to connect a pedal unit;
• the pedal unit is configured to detachably attach to the receiving member;
• a chain threaded between the pedal unit and a rear wheel;
• wherein the pedal unit rotatably retains a pedal crank comprising an axially attached chain wheel and incorporates a connector configured to connect to the receiving member, and the chain is configured to attachably/detachably connect the pedal unit and chain to the bicycle frame upon being wrapped around the chain wheel and a rear sprocket installed on the rear wheel;
• and
• wherein the bicycle frame comprises seat stays on both sides of the rear wheel, and the bicycle frame is configured to enable a seat stay only on a side of the chain wheel to be freely attached to and detached from the bicycle frame;
• wherein the bicycle frame comprises, at least on a chain wheel side of the bicycle frame, a chain stay that rotatably fastens the rear wheel;
• wherein the chain stay comprises a forward-upwardly extending inclined branch towards a rear wheel side end of the chain stay on the side of the chain wheel;
• wherein a rear end side of the seat stay on the side of the chain wheel is being fastened to the forward-upwardly extending inclined branch of the chain stay;
• and
• wherein the pedal unit is equipped with a chain cover that covers the chain entirely, and the forward-upwardly extending inclined branch of the chain stay is provided outside the chain cover so as to overlap the chain cover in side view of the bicycle frame.