PURPOSE: To measure the state of web irregularity without contact with a high precision by arranging plural photoelectric detectors in the card width direction and using obtained electric signals.

CONSTITUTION: Plural light flux projection equipments 51 to 5n and plural light receiving equipments 71 to 7n are arranged in the upper side of web 4 and the lower side of web 4 respectively between doffing unit 2, which takes off web 4 from doffer 1 and transfers it, and calender roller 3 which makes web 4 into a silver and pulls out it. Through light fluxes 61 to 6n from projection equipments 51 to 5n reach light receiving equipments 71 to 7n through web 4, they have intensity changed according to the thickness of web 4, and electric signals according to light quantities of light receiving equipments 71 to 7n are generated. The average value in each measuring point is calculated from values of them, thereby detecting the state of web irregularity.