The present invention provides a device for treating substrate which adopts a stable substrate joining interval for conveying the substrate to a float table through a flat type conveying, wherein, the interval does not be effected by thermal expansion or shrink of the float table caused by a temperature change. A pre-bake unit (48) carries with a roller conveying part (126) for joining the substrate on a beginning end part (100b) which locates on the float table (100) of a substrate conveying line and is more close to outside than a float surface (100a). Preferably, the roller conveying part (126) collocates a plurality of dreidel-shaped free rollers (128) to a column in a width direction (Y direction) of a table orthogonal to the substrate conveying line. The substrate (G) moves horizontally above a drive roller conveying part (82) on an upstream side and the free rollers (128) of the beginning end part (100b) of the float table by a roller conveying method, simultaneously, is conveyed to the float table.