Composition for solid washing agent, and solid washing agent

A composition for a solid washing agent that is highly foaming yet hard even in a high-temperature, high humidity environment, comprising:

• an N-long chain acyl acidic amino acid salt as a component of an ingredient,
• a salt for the N-long chain acyl acidic amino acid salt comprising an alkali metal salt and an ethanolamine salt,
• a molar ratio of the alkali metal salt to the ethanolamine salt being 10:90 to 75:25,
• a degree of neutralization being 1.5 to 2.0 eq, and
• an alkyl-modified silicone represented by formula (I) below as an ingredient:
• wherein R represents an alkyl or alkenyl group having 8 to 18, and a and b each represent an integer of 0 to 3;
• wherein the composition has a maximum extent of melting caused by rubbing of 70 g/100 cm2 as determined according to JIS K-3304 and has foaming properties of at least 1950 ml as determined by stirring 400 ml of 1 wt % in aqueous 70 ppm calcium chloride at 40 degrees Centigrade for 60 seconds.