Apparatus (7; 112) for controlling the conditions of at least one band (4; 103, 104, 105, 106) circulating in a paper making machine (1; 100) along a circulating direction (d1; R1, R2, R3, R4); the apparatus (7; 112) comprising: - at least one first detecting device (28; 163, 164, 165, 166) configured to detect at least one first parameter indicative of humidity (U1; U1-1, U1-2, U1-3, U1-4) of the band (4; 103, 104, 105, 106) and positionable in a first position (b1; b3, b4, b5, b6) between a pressing station (13; 130, 134, 132) and a conditioning station (14; 143, 144, 145, 146) of the paper making machine (1; 100); - at least one second detecting device (29; 173, 174, 175, 176) configured to detect at least one second parameter indicative of humidity (U2; U2-1, U2-2, U2-3, U2-4) of the band (4; 103, 104, 105, 106) and positionable in a second position (b2; c3, c4, c5, c6) downstream of the conditioning station (14; 143, 144, 145, 146) of the paper making machine (1; 100), characterized by - at least one third detecting device (30; 183, 184, 185) configured to detect at least one third parameter indicative of the humidity (U3; U3-1, U3-2, U3-3) of the band (4; 103, 104, 105,) and of the paper sheet (3, 99) and positionable in a third position (b3; d3, d4, d5) upstream of the pressing station (13; 130, 134), and - a processing unit (34; 190) configured to calculate at least one datum (D1, D2, D3...Dn; E1, E2, E3...En) indicative of the condition of the band (4; 103, 104, 105, 106) on the basis of the first parameter indicative of humidity (U1; Ul-1, Ul-2, Ul-3, Ul-4),of the second parameter indicative of humidity (U2; U2-1, U2-2, U2-3, U2-4) and of the third parameter indicative of the humidity (U3; U3-1, U3-2, U3-3) of the band (4; 103, 104, 105,) and of the paper sheet (3, 99). - at least one first detecting device (28; 163, 164, 165, 166) configured to detect at least one first parameter indicative of humidity (U1; U1-1, U1-2, U1-3, U1-4) of the band (4; 103, 104, 105, 106) and positionable in a first position (b1; b3, b4, b5, b6) between a pressing station (13; 130, 134, 132) and a conditioning station (14; 143, 144, 145, 146) of the paper making machine (1; 100); - at least one second detecting device (29; 173, 174, 175, 176) configured to detect at least one second parameter indicative of humidity (U2; U2-1, U2-2, U2-3, U2-4) of the band (4; 103, 104, 105, 106) and positionable in a second position (b2; c3, c4, c5, c6) downstream of the conditioning station (14; 143, 144, 145, 146) of the paper making machine (1; 100), characterized by - at least one third detecting device (30; 183, 184, 185) configured to detect at least one third parameter indicative of the humidity (U3; U3-1, U3-2, U3-3) of the band (4; 103, 104, 105,) and of the paper sheet (3, 99) and positionable in a third position (b3; d3, d4, d5) upstream of the pressing station (13; 130, 134), and - a processing unit (34; 190) configured to calculate at least one datum (D1, D2, D3...Dn; E1, E2, E3...En) indicative of the condition of the band (4; 103, 104, 105, 106) on the basis of the first parameter indicative of humidity (U1; Ul-1, Ul-2, Ul-3, Ul-4),of the second parameter indicative of humidity (U2; U2-1, U2-2, U2-3, U2-4) and of the third parameter indicative of the humidity (U3; U3-1, U3-2, U3-3) of the band (4; 103, 104, 105,) and of the paper sheet (3, 99).