A powder surface-treated with an organopolysiloxane represented by the following average compositional formula (1): R1aR2bR3cSiO(4-a-b-c)/2  (1) wherein R1 is selected from the group consisting of C1-30 alkyl, C1-30 fluoroalkyl, C6-30 aryl, and C6-30 aralkyl groups, R2 is a group represented by the following formula (2), provided that R2 is bonded to at least one terminal end of the organopolysiloxane when c equals 0, R3 is a group represented by the following formula (3): wherein R2 is as defined above, each R8 is, independently, selected from the group consisting of C1-30 alkyl, C1-30 fluoroalkyl, C6-30 aryl, and C6-30 aralkyl groups, Q is CdH2d or an oxygen atom, wherein d is an integer of from 1 to 5, k is an integer of from 0 to 500, and h is an integer of from 0 to 3, a is a number of from 1.5 to 2.5, b is a number of from 0.001 to 1.5, and c is a number of from 0 to 1.5.