A multiple optical axis photoelectric sensor for detecting an object to be detected, which is conveyed by a conveyance device, the multiple optical axis photoelectric sensor comprising: a light projecting device having a plurality of light projecting sections which are arrayed in a line, a light receiving device having a plurality of light receiving sections which are disposed to face the light projecting sections, a light blocking determination section configured to perform a light blocking determination of whether or not any optical axes formed between opposed light projecting sections and light receiving sections are in a light blocking state, an output section configured to output a detection signal on the basis of a result of the light blocking determination, and a muting processing section configured to perform muting so as not to output the detection signal even though a subset or all of the optical axes are in a light blocking state, wherein the muting processing section comprises: a muting initiating section configured to initiate the muting of the optical axes in a first range in response to a signal input from an external muting device indicating that the object to be detected is conveyed toward the multiple optical axis photoelectric sensor, and a muting altering section configured to select, as the optical axis to be muted thereafter, the optical axes in a second range that includes all blocked optical axes of the first range, wherein the muting altering section is configured to select the optical axis in the second range depending on the light blocking state of the optical axes in the first range while the optical axes in the first range are muted and that the muting altering section is configured to acquire the range of the blocked optical axes during an acquisition period for acquiring a blocked light range. a light projecting device having a plurality of light projecting sections which are arrayed in a line, a light receiving device having a plurality of light receiving sections which are disposed to face the light projecting sections, a light blocking determination section configured to perform a light blocking determination of whether or not any optical axes formed between opposed light projecting sections and light receiving sections are in a light blocking state, an output section configured to output a detection signal on the basis of a result of the light blocking determination, and a muting processing section configured to perform muting so as not to output the detection signal even though a subset or all of the optical axes are in a light blocking state, wherein the muting processing section comprises: a muting initiating section configured to initiate the muting of the optical axes in a first range in response to a signal input from an external muting device indicating that the object to be detected is conveyed toward the multiple optical axis photoelectric sensor, and a muting altering section configured to select, as the optical axis to be muted thereafter, the optical axes in a second range that includes all blocked optical axes of the first range, wherein the muting altering section is configured to select the optical axis in the second range depending on the light blocking state of the optical axes in the first range while the optical axes in the first range are muted and that the muting altering section is configured to acquire the range of the blocked optical axes during an acquisition period for acquiring a blocked light range. a muting initiating section configured to initiate the muting of the optical axes in a first range in response to a signal input from an external muting device indicating that the object to be detected is conveyed toward the multiple optical axis photoelectric sensor, and a muting altering section configured to select, as the optical axis to be muted thereafter, the optical axes in a second range that includes all blocked optical axes of the first range, wherein the muting altering section is configured to select the optical axis in the second range depending on the light blocking state of the optical axes in the first range while the optical axes in the first range are muted and that the muting altering section is configured to acquire the range of the blocked optical axes during an acquisition period for acquiring a blocked light range.