A membrane cartridge constituting a submerged membrane separator, the membrane cartridge comprising: a filtration membrane provided at least on one surface of a filtration plate; channel groove patterns (38, 39) formed on the surface of the filtration plate covered with the filtration membrane, the channel groove patterns (38, 39) allowing passage of a permeated liquid having passed through the filtration membrane; and permeated liquid outlets (41, 42, 66, 67) provided on a circumferential edge of the filtration plate, the permeated liquid outlets (41, 42, 66, 67) collecting and taking out the permeated liquid having passed through the channel groove patterns (38, 39), wherein the filtration plate is divided into multiple water collection sections (44 - 49), the channel groove patterns (38, 39) are formed in the respective water collection sections (44 - 49), the channel groove patterns include a first channel groove pattern and a second channel groove pattern, wherein the first channel groove patterns is formed in one of the collection sections (44 - 49) and the second channel groove pattern is formed in another one of the central water collection sections (44 - 49), a length direction of the through channel grooves in the first channel groove pattern and a length direction of the through-channel grooves in the second channel groove pattern are different from each other, a header groove (51 - 53) is provided at a boundary portion of the water collection sections (44 - 49), the header groove (51 - 53) has a larger channel cross-sectional area than the through-channel grooves (38a, 39a), the through-channel grooves (38a, 39a) in one of the water collection sections (44 - 49) and the through-channel grooves (38a - 39a) in another one of the water collection sections (44 - 49) adjacent to the one of the water collection sections communicate with the header groove (51 - 53) through the boundary portion, the respective through-channel grooves (38a, 39a) gradually approach one of the permeated liquid outlets (41, 42, 66, 67) nearest to the water collection section (44 - 49) to which the respective through-channel grooves (38a, 39a) belong from one end to the other end, characterized in that the header groove (51 - 53) communicates directly with a hole of one of the permeated liquid outlets (41, 42, 66, 67) and the channel groove patterns (38, 39) including linear through-channel grooves (38a, 39a) across the water collection sections (44 - 49). a filtration membrane provided at least on one surface of a filtration plate; channel groove patterns (38, 39) formed on the surface of the filtration plate covered with the filtration membrane, the channel groove patterns (38, 39) allowing passage of a permeated liquid having passed through the filtration membrane; and permeated liquid outlets (41, 42, 66, 67) provided on a circumferential edge of the filtration plate, the permeated liquid outlets (41, 42, 66, 67) collecting and taking out the permeated liquid having passed through the channel groove patterns (38, 39), wherein the filtration plate is divided into multiple water collection sections (44 - 49), the channel groove patterns (38, 39) are formed in the respective water collection sections (44 - 49), the channel groove patterns include a first channel groove pattern and a second channel groove pattern, wherein the first channel groove patterns is formed in one of the collection sections (44 - 49) and the second channel groove pattern is formed in another one of the central water collection sections (44 - 49), a length direction of the through channel grooves in the first channel groove pattern and a length direction of the through-channel grooves in the second channel groove pattern are different from each other, a header groove (51 - 53) is provided at a boundary portion of the water collection sections (44 - 49), the header groove (51 - 53) has a larger channel cross-sectional area than the through-channel grooves (38a, 39a), the through-channel grooves (38a, 39a) in one of the water collection sections (44 - 49) and the through-channel grooves (38a - 39a) in another one of the water collection sections (44 - 49) adjacent to the one of the water collection sections communicate with the header groove (51 - 53) through the boundary portion, the respective through-channel grooves (38a, 39a) gradually approach one of the permeated liquid outlets (41, 42, 66, 67) nearest to the water collection section (44 - 49) to which the respective through-channel grooves (38a, 39a) belong from one end to the other end, characterized in that the header groove (51 - 53) communicates directly with a hole of one of the permeated liquid outlets (41, 42, 66, 67) and the channel groove patterns (38, 39) including linear through-channel grooves (38a, 39a) across the water collection sections (44 - 49).