A game controller configured to be removably attached to a main unit of a portable gaming device and adapted to be operated in at least a portrait position and a landscape position, the game controller comprising: a housing having a shape elongated in a predetermined direction, the housing having a primary surface, at least one first side surface extending in the predetermined direction, and at least one second side surface different from the at least one first side surface, the at least one second side surface extending in the predetermined direction, wherein the at least one first side surface is adapted to be attached to and detached from the main unit; a directional input section on the primary surface of the housing; a first operation section and a second operation section on one of the at least one first side surface, wherein the first operation section is on one side of a center of the first side surface with respect to the predetermined direction and the second operation section is on the other side of the center of the first side surface with respect to the predetermined direction allowing operation of the first operation section and the second operation section respectively by a left and a right index finger of the user, when the housing is held in the landscape position by both hands of the user so as to allow operation of the directional input section by a thumb; a third operation section and a fourth operation section on a corner portion of the housing at one of two ends in the predetermined direction of one of the at least one second side surface away from the first side surface allowing operation of the third operation section and the fourth operation section by an index finger of a user, when the housing is held in the portrait position in one hand of the user so as to allow operation of the directional input section by a thumb, wherein: the housing has a rounded shape in the corner portion; and the third operation section and the fourth operation section each have a rounded shape in conformity with the rounded shape of the housing, and wherein the corner portion has a more rounded shape than a corner portion of the housing at one of the ends of the first side surface. a housing having a shape elongated in a predetermined direction, the housing having a primary surface, at least one first side surface extending in the predetermined direction, and at least one second side surface different from the at least one first side surface, the at least one second side surface extending in the predetermined direction, wherein the at least one first side surface is adapted to be attached to and detached from the main unit; a directional input section on the primary surface of the housing; a first operation section and a second operation section on one of the at least one first side surface, wherein the first operation section is on one side of a center of the first side surface with respect to the predetermined direction and the second operation section is on the other side of the center of the first side surface with respect to the predetermined direction allowing operation of the first operation section and the second operation section respectively by a left and a right index finger of the user, when the housing is held in the landscape position by both hands of the user so as to allow operation of the directional input section by a thumb; a third operation section and a fourth operation section on a corner portion of the housing at one of two ends in the predetermined direction of one of the at least one second side surface away from the first side surface allowing operation of the third operation section and the fourth operation section by an index finger of a user, when the housing is held in the portrait position in one hand of the user so as to allow operation of the directional input section by a thumb, wherein: the housing has a rounded shape in the corner portion; and the third operation section and the fourth operation section each have a rounded shape in conformity with the rounded shape of the housing, and wherein the corner portion has a more rounded shape than a corner portion of the housing at one of the ends of the first side surface. the housing has a rounded shape in the corner portion; and the third operation section and the fourth operation section each have a rounded shape in conformity with the rounded shape of the housing, and wherein the corner portion has a more rounded shape than a corner portion of the housing at one of the ends of the first side surface.