A sigmoidoscope comprising: a main body having an optic head having a channel extending through the optic head ; and a positioning recess disposed at a middle portion of the optic head ; a handle connected to the optic head and having a chamber communicating with the channel ; and an illuminating assembly having a circuit board disposed in the positioning recess and having an annular outline; and a central hole aligned with the channel ; multiple light emitting elements annularly mounted to the circuit board at intervals and electrically connected to the circuit board ; two wires electrically connected to the circuit board ; two electrodes respectively and electrically connected to the two wires ; and at least one battery electrically connecting the two electrodes , the sigmoidoscope being further characterized by having a tact switch mounted to the circuit board , electrically connected to the circuit board and by having a pushing button extending over a rim of the central hole and being able to be pressed by an inserting tube of a speculum assembly that is inserted into the central hole . a main body having an optic head having a channel extending through the optic head ; and a positioning recess disposed at a middle portion of the optic head ; a handle connected to the optic head and having a chamber communicating with the channel ; and an optic head having a channel extending through the optic head ; and a positioning recess disposed at a middle portion of the optic head ; a channel extending through the optic head ; and a positioning recess disposed at a middle portion of the optic head ; a handle connected to the optic head and having a chamber communicating with the channel ; and an illuminating assembly having a circuit board disposed in the positioning recess and having an annular outline; and a central hole aligned with the channel ; multiple light emitting elements annularly mounted to the circuit board at intervals and electrically connected to the circuit board ; two wires electrically connected to the circuit board ; two electrodes respectively and electrically connected to the two wires ; and at least one battery electrically connecting the two electrodes , the sigmoidoscope being further characterized by having a tact switch mounted to the circuit board , electrically connected to the circuit board and by having a pushing button extending over a rim of the central hole and being able to be pressed by an inserting tube of a speculum assembly that is inserted into the central hole . a circuit board disposed in the positioning recess and having an annular outline; and a central hole aligned with the channel ; an annular outline; and a central hole aligned with the channel ; multiple light emitting elements annularly mounted to the circuit board at intervals and electrically connected to the circuit board ; two wires electrically connected to the circuit board ; two electrodes respectively and electrically connected to the two wires ; and at least one battery electrically connecting the two electrodes , the sigmoidoscope being further characterized by having a tact switch mounted to the circuit board , electrically connected to the circuit board and by having a pushing button extending over a rim of the central hole and being able to be pressed by an inserting tube of a speculum assembly that is inserted into the central hole . <EOS>