To provide a hydrostatic transmission device applied to a tractor, a riding lawn mower, lawn and gardening instruments, and the like mainly in lawn and garden industry.

The hydrostatic transmission device is provided with a fluid motor and a variable discharge fluid pump in fluid communication with the motor and having a first discharge rate and a higher second discharge rate. The pump is mounted on a block. The block has an outer surface, a passage for a fluid to flow from the pump to the motor, and first and second fluid bleeding holes extending from the passage to the outer surface. When the pump is operated at the first rate and a sliding element is in a first position, the passage and a fluid reservoir part on the outside of the pump are in fluid communication with each other through the bleeding holes and the hollow of the sliding element arranged in the hole of the block. When the pump is operated at the second rate and the sliding element is in a second position, the first bleeding hole and the fluid reservoir part are not substantially in fluid communication with each other.