The present invention provides an incubator which can release pressure applied to a vessel side by upper heating means, and can simplify an opening/closing structure of a reaction chamber. The gist of the present invention resides in an incubator comprising a reaction chamber disposed in an incubator body; a heat conductive reaction block disposed in the reaction chamber to hold one or plural vessels containing reaction samples; a cover for covering an upper part of the reaction chamber in an openable manner; upper heating means positioned on a lower surface of the cover to heat an upper part of the vessel held by the reaction block; and pressure means for pressing the upper heating means to the vessel side; the reaction block being heated/cooled while the upper part of the vessel is heated by the upper heating means, to incubate the reaction sample; wherein the cover is disposed rotatably and movably in a horizontal direction with respect to the incubator body.