To provide a bicycle bottom bracket structure which has a power generating mechanism capable of generating energy sufficient to actuate one or a plurality of electrically powered equipment.

The bottom bracket structure 12 has a dynamo 28 which generates electricity when a rider pedals a bicycle. The dynamo 28 has a fixed part which is fixed to a part of the frame of the bicycle, and a rotary part which is connected rotatably to a fixed part of the frame of the bicycle. The rotary part of the dynamo is connected to a shaft part 22 of the bottom bracket structure 12 via a planetary gear unit 30, which so connects the shaft part 22 and the rotary part of the dynamo 28 that the rotary part of the dynamo 28 rotates faster than the shaft part 22.