Provided is a solid puzzle block (1) . The solid puzzle block has a connecting groove (13 and 33) open from the top to the bottom of a side surface (11 and 31) of its main body to allow cross-connecting of two blocks, and a connecting peg (14) and connecting hole (15) formed at either end of the connecting groove (13) on the side surface (11 and 31) to allow side-connecting of two blocks. In order to impart a firm cross-connection, a plurality of embossings (12) are formed on the left and right surfaces of the connecting groove (13 and 33) and the contact portions (42) of the upper and lower surfaces (40 and 41) contacting the connecting groove (13 and 33) . At an end surface (16 and 36) between the left and right surfaces of the connecting groove (13 and 33) is fixed a connector (17), to which an operating unit (21) located inside the main body is connected electrically. Although the firmly connecting block is not of an assorted variety, it can arouse enjoyment and curiosity in users of all ages.