A refrigerator comprises a cassette accommodating section which is enclosed by a wall, kept at a low temperature, and capable of accommodating a film feed cassette in such a way that it can be released therefrom. The film feed cassette houses therein a long test film containing a reagent which will react with a liquid sample and give rise to a change in optical density. The film feed cassette has a film outlet through which the long test film is fed out. The refrigerator has a film outlet which is formed in the wall at a position corresponding to the position of the film outlet of the film feed cassette and through which the long test film is pulled out. An air stream jetting system jets dry air to the surface of the portion of the long test film positioned between the film outlet of the film feed cassette and the film outlet of the refrigerator. The air stream jetting system comprises a device wherein two air drying chambers are alternately operated, which allows dry air to be generated approximately continuously, and wet air does not enter a dry air feed-out path even for an instant.