The invention relates to a novel infinitely-variable-speed belt wheel device, and belongs to the mechanical field. The device comprises brake handles, a brake handle rotary shaft, a drive belt wheel, a general supporting plate, a drive belt wheel shaft, a belt wheel connector, hydraulic supporting rods, a brake disc gear, a hydraulic cylinder, a hydraulic supporting transverse rod, a driven wheel shaft, a driven wheel, a bracket wheel disc, a fixed threaded sleeve, a rotary gear shaft and drive wheel fixed connectors, wherein the hydraulic cylinder is a constant-pressure type hydraulic cylinder, and supporting force, on the drive belt wheel, of the hydraulic cylinder is constant; and the hydraulic cylinder also can be shortened as a result of stress of the drive belt wheel. Each part of the drive belt wheel can move in the radial direction due to a mode that the rotary gear shaft rotates around the fixed threaded sleeve, so that a transmission ratio is changed, and rotation speed of the driven wheel is changed in case of keeping rotation speed of the drive wheel unchanged. The brake disc gear and the drive belt wheel rotate at the same angular velocity when the brake handles are not pressed down; when the brake handles are pressed down, the rotary gear shaft is in engaged rotation with the brake disc gear, and the drive belt wheel extends in the radial direction; and two pairs of brake handles are arranged, so that the diameter of the drive belt wheel is reduced. The device can be mounted in a using occasion that rotation speed of the driven belt wheel needs to frequently change, and torque of the driven belt wheel is not very great, for example metallurgy and assembly line plant.