Hydroxyalkyl alkyl cellulose, method for producing the same, and solid preparation

A hydroxyalkyl alkyl cellulose having a volume-based average particle size, determined by dry laser diffractometry, of more than 100 μm and not more than 150 μm;

• and having, on a basis of a dynamic image analysis to divide all particles into fine particles, spherical particles and fibrous particles, a volume fraction of the fibrous particles relative to all of the particles of more than 40% and not more than 50%, and a volume fraction of the fine particles relative to all of the particles of less than 2.0%;
• wherein
• the fine particles have a length of fiber of less than 40 μm, and
• the fibrous particles have a length of fiber of 40 μm or more and are particles other than the spherical particles consisting of first and second spherical particles, wherein the first spherical particles have an elongation, which is a ratio of a diameter of fiber to a length of fiber, of 0.5 or more, and the second spherical particles have an elongation of less than 0.5, an aspect ratio, which is a ratio of a maximal Feret diameter to a minimal Feret diameter, of 0.5 or more, and a circularity, which is a ratio of a perimeter (PEQPC) of a circle that has the same area as a projection area to a perimeter (Preal) of a real particle, of 0.7 or more.