To cut an installation cost and a heat-up time and thereby make it easy to perform the expanding process of a bamboo by passing the bamboo split longitudinally into plural pieces to the specified length with joints both inner and outer removed, through an expansion part equipped with a a set of rolls, upper and lower, of a different shape from each other, a heating plate on a running plane and a lifting mechanism to obtain bamboo boards through manipulating the heater and an exhaust fan.

A heating part 6 is equipped with a heater 16 consisting of an electromagnetic wave transmitter, waveguides 17 or the like mounted on the top of a mobile part 5, and the responsive blocking of a passageway 15 and the starting/stoppage of the heater 16 are controlled by a signal from a detection part 7 which detects the approach and moving-away of bamboos split longitudinally into plural pieces to the length of 20 cm or more with joints both inner and outer removed, at a spot before the outlet of each of the waveguides 17. In the passageway 15, a stirring 18 and a duct 19 which guides water vapors generated from a raw material at the time of heating and an exhaust means 20 are provided. An expansion part 9 holding a roller conveyor 8 has a set of rolls, upper and lower, differing in shape arranged above and under a frame 4. The upper rolls having no counter-rolls have a disposed heating element-incorporated heating plate 33. The right/left bearings 39 of each of the rolls are suspended by each of lifting plates 40 so that the smooth operation to apply and remove a pressure is carried out.