To provide a hollow block capable of shortening time of masonry work without leaking concrete to the outside and facilitating block masonry by everybody.

A hollow block is constituted of a pair of face shells 2 and 2 opposed to each other and a plurality of webs 3 built between a pair of face shells 2 and 2. In an upper edge section of each of a pair of face shells 2, an outside edge section is used for an outside sheathing 7 formed higher than an inside edge section thereof, and in a lower edge section of each of a pair of face shells 2, the inside edge section is formed higher than the outside edge section, and it is used for an inside sheathing 8 capable of interlocking with the outside sheathing 7. Grooves 6 and 6 are formed along up and down directions in both end faces in the longitudinal direction of each of the face shells 2. For that purpose, time of masonry work can be reduced, and anybody can facilitate masonry work.