WE CLAIM:
1. A method of producing cellulase comprising the following steps of (1)
to (3):
(1) the step of subjecting an aqueous solution of cellulase derived from filamentous fungi to liquid-liquid filtration through an ultrafiltration membrane with a molecular weight cut off of 100,000 to 200,000 to obtain a filtrate and to concurrently obtain a concentrated enzyme solution as a retentate;
(2) the step of further subjecting the filtrate obtained in the step (1) to filtration through a second ultrafiltration membrane with a molecular weight cut off of 5,000 to 50,000 to obtain a second concentrated enzyme solution as a retentate; and
(3) the step of mixing the concentrated enzyme solution obtained in the steps of (1) and (2) to obtain cellulase derived from filamentous fungi,
wherein said filamentous fungi is a microorganism selected from the genus Aspergillus, the genus Cellulomonas, the genus Clostridium, the genus Streptomyces, the genus Acremonium, the genus Irpex, the genus Mucor, the genus Talaromyces, the genus Sulofolobus, the genus Thermoplasma, the genus Caldivirgra, the genus Thermosphaera, the genus Pyrococcus, the genus Picrophilus, the genus Caldivirgra, the genus Fervidobacterium or Trichoderma.
2. The method of producing cellulase as claimed in claim 1, wherein said
filamentous fungi is Trichoderma.

3. The method of producing cellulase as claimed in claim 1 or 2, wherein said aqueous solution of cellulase derived from filamentous fungi is adjusted to pH 2.6 to 5.4 or pH 8.6 to 9.4 in the step (1).
4. The method of producing cellulase as claimed in any of claims 1 to 3, wherein said aqueous solution of cellulase derived from filamentous fungi is a filamentous fungi culture liquid or a hydrolysate of biomass containing cellulose obtained by using said cellulase derived from filamentous fungi.
5. The method of producing cellulase as claimed in any of claims 1 to 4, wherein said aqueous solution of cellulase derived from filamentous fungi comprises one or more enzyme components selected from the group consisting of cellobiohydrolase, endoglucanase, and xylanase.
6. The method of producing cellulase as claimed in any of claims 1 to 5, wherein a temperature of said aqueous solution of cellulase derived from filamentous fungi is in a temperature range of 15 to 35oC.