Abstract: A seeding machine comprises: an air compressor for generating a positive air pressure; a soil hardness sensor for measuring soil hardness so as to produce a control signal to adjust the positive air pressure generated by the compressor; an air pressure adjuster for adjusting the positive air pressure generated by the air compressor in accordance with the control signal produced by the soil hardness sensor; a negative air pressure generator for generating a negative air pressure by making use of air under the positive air pressure; a change-over valve for effecting a change-over operation between the positive air pressure and the negative air pressure, so as to selectively supply the positive air pressure or the negative air pressure; a seed adsorber for catching a seed by virtue of the negative air pressure; a first air cylinder adapted to extend or contract by the positive air pressure, to cause a certain reciprocating movement of the seed adsorber; a second air cylinder adapted to extend or contract by the